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Message-ID: <x2qaf41c7c41004061000q688d8782tde8702b62cdd5d9b@mail.gmail.com>
Date: Tue, 6 Apr 2010 10:00:07 -0700
From: Divyesh Shah <dpshah@...gle.com>
To: Vivek Goyal <vgoyal@...hat.com>
Cc: jens.axboe@...cle.com, linux-kernel@...r.kernel.org,
nauman@...gle.com, ctalbott@...gle.com
Subject: Re: [PATCH 2/3][v2] blkio: Add io controller stats like
On Tue, Apr 6, 2010 at 6:47 AM, Vivek Goyal <vgoyal@...hat.com> wrote:
> On Mon, Apr 05, 2010 at 04:29:06PM -0700, Divyesh Shah wrote:
>> On Mon, Apr 5, 2010 at 9:06 AM, Vivek Goyal <vgoyal@...hat.com> wrote:
>> > On Fri, Apr 02, 2010 at 06:56:35PM -0700, Divyesh Shah wrote:
>> >> - io_service_time (the actual time in ns taken by the dis to service the IO)
>> >> - io_wait_time (the time spent waiting in the IO shceduler queues before
>> >> getting serviced)
>> >> - io_serviced (number of IOs serviced from this blkio_group)
>> >> - io_service_bytes (Number of bytes served for this cgroup)
>> >>
>> >> These stats are accumulated per operation type helping us to distinguish between
>> >> read and write, and sync and async IO. This patch does not increment any of
>> >> these stats.
>> >>
>> >> Signed-off-by: Divyesh Shah<dpshah@...gle.com>
>> >> ---
>> >>
>> >> Documentation/cgroups/blkio-controller.txt | 33 +++++
>> >> block/blk-cgroup.c | 179 +++++++++++++++++++++++++---
>> >> block/blk-cgroup.h | 41 +++++-
>> >> block/cfq-iosched.c | 2
>> >> 4 files changed, 229 insertions(+), 26 deletions(-)
>> >>
>> >> diff --git a/Documentation/cgroups/blkio-controller.txt b/Documentation/cgroups/blkio-controller.txt
>> >> index 630879c..ededdca 100644
>> >> --- a/Documentation/cgroups/blkio-controller.txt
>> >> +++ b/Documentation/cgroups/blkio-controller.txt
>> >> @@ -75,6 +75,9 @@ CONFIG_DEBUG_BLK_CGROUP
>> >>
>> >> Details of cgroup files
>> >> =======================
>> >> +Writing an int to any of the stats files (which excludes weight) will result
>> >> +in all stats for that cgroup to be erased.
>> >> +
>> >> - blkio.weight
>> >> - Specifies per cgroup weight.
>> >>
>> >> @@ -92,6 +95,36 @@ Details of cgroup files
>> >> third field specifies the number of sectors transferred by the
>> >> group to/from the device.
>> >>
>> >> +- blkio.io_service_bytes
>> >> + - Number of bytes transferred to/from the disk by the group. These
>> >> + are further divided by the type of operation - read or write, sync
>> >> + or async. First two fields specify the major and minor number of the
>> >> + device, third field specifies the operation type and the fourth field
>> >> + specifies the number of bytes.
>> >> +
>> >> +- blkio.io_serviced
>> >> + - Number of IOs completed to/from the disk by the group. These
>> >> + are further divided by the type of operation - read or write, sync
>> >> + or async. First two fields specify the major and minor number of the
>> >> + device, third field specifies the operation type and the fourth field
>> >> + specifies the number of IOs.
>> >> +
>> >> +- blkio.io_service_time
>> >> + - Total amount of time spent by the device to service the IOs for this
>> >> + cgroup. This is in nanoseconds to make it meaningful for flash
>> >> + devices too. This time is further divided by the type of operation -
>> >> + read or write, sync or async. First two fields specify the major and
>> >> + minor number of the device, third field specifies the operation type
>> >> + and the fourth field specifies the io_service_time in ns.
>> >
>> > Hi Divyesh,
>> >
>> > Looking the third patch where you acutally increment the stats, this is
>> > how service time is calculated.
>> >
>> > - Save start_time in rq, when driver actually removes the request from
>> > request queue.
>> > - at request completion time calculate service time.
>> > service_time = now - start_time.
>> >
>> > This works very well if driver/device does not have NCQ and process one
>> > request at a time. But with NCQ, we can multiple requests in the driver
>> > queue at the same time then we can run into issues.
>> >
>> > - With NCQ, time becomes cumulative. So if three requests rq1, rq2 and rq3
>> > are in disk queue, and if requests are processed in the order rq1,rq2,rq3 by
>> > the disk (no parallel channles), then rq1 and rq2's completion time is
>> > added in rq3. So total service time of the group can be much more than
>> > actual time elapsed. That does not seem right. Did you face this issue in
>> > your testing?
>>
>> You are right. With NCQ, the io_service_time numbers aren't exact.
>> I've only tested this without NCQ for which these stats are accurate
>> and very useful. With NCQ turned on I don't see a good way of getting
>> this information accurately since only the disk knows when it actually
>> starts to service a given request. With NCQ, io_service_time will have
>> cumulative time as you pointed out which may still be useful for some
>> high-level analysis if you also have the average queue depth for the
>> device.
>>
>
> Most of the modern disks now seem to be be NCQ. But I guess we can keep
> those stats as it is useful for you on non NCQ setup.
>
>> io_wait_time stat makes sense with or w/o NCQ since its defined to
>> only include the scheduler queueing time for each IO and is cumulative
>> by design. I should probably reword the definition of io_service_time
>> to indicate time after dispatch to the driver and request completion
>> and also add a comment of how NCQ affects this stat. Sounds good?
>
> I am not sure if io_wait_time is cumulative by design. Think of this,
> somebody says that this cgroup has waited for 1s on CFQ queue but actually
> only .5 seconds have elapsed since the observation started.
>
> So I would say that please document it very properly in blkio-controller.txt
> so that it is clear what exactly these numbers represent and what to expect on
> NCQ disks.
Ok I will try to clarify further.
>
> Thanks
> Vivek
>
>>
>> -Divyesh
>>
>> >
>> > Same is the case with io_wait_time, Because time is cumulative, actual
>> > io_wait_time, can be more than real time elapsed.
>> >
>> > Is this the intention and you are finding even cumulative time useful?
>> >
>> >> +
>> >> +- blkio.io_wait_time
>> >> + - Total amount of time the IO spent waiting in the scheduler queues for
>> >> + service. This is in nanoseconds to make it meaningful for flash
>> >> + devices too. This time is further divided by the type of operation -
>> >> + read or write, sync or async. First two fields specify the major and
>> >> + minor number of the device, third field specifies the operation type
>> >> + and the fourth field specifies the io_wait_time in ns.
>> >> +
>> >> - blkio.dequeue
>> >> - Debugging aid only enabled if CONFIG_DEBUG_CFQ_IOSCHED=y. This
>> >> gives the statistics about how many a times a group was dequeued
>> >> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c
>> >> index 5be3981..cac10b2 100644
>> >> --- a/block/blk-cgroup.c
>> >> +++ b/block/blk-cgroup.c
>> >> @@ -17,6 +17,8 @@
>> >> #include <linux/err.h>
>> >> #include "blk-cgroup.h"
>> >>
>> >> +#define MAX_KEY_LEN 100
>> >> +
>> >> static DEFINE_SPINLOCK(blkio_list_lock);
>> >> static LIST_HEAD(blkio_list);
>> >>
>> >> @@ -55,12 +57,15 @@ struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup)
>> >> }
>> >> EXPORT_SYMBOL_GPL(cgroup_to_blkio_cgroup);
>> >>
>> >> -void blkiocg_update_blkio_group_stats(struct blkio_group *blkg,
>> >> - unsigned long time)
>> >> +void blkiocg_update_timeslice_used(struct blkio_group *blkg, unsigned long time)
>> >> {
>> >> - blkg->time += time;
>> >> + unsigned long flags;
>> >> +
>> >> + spin_lock_irqsave(&blkg->stats_lock, flags);
>> >> + blkg->stats.time += time;
>> >> + spin_unlock_irqrestore(&blkg->stats_lock, flags);
>> >> }
>> >> -EXPORT_SYMBOL_GPL(blkiocg_update_blkio_group_stats);
>> >> +EXPORT_SYMBOL_GPL(blkiocg_update_timeslice_used);
>> >>
>> >> void blkiocg_add_blkio_group(struct blkio_cgroup *blkcg,
>> >> struct blkio_group *blkg, void *key, dev_t dev)
>> >> @@ -170,13 +175,119 @@ blkiocg_weight_write(struct cgroup *cgroup, struct cftype *cftype, u64 val)
>> >> return 0;
>> >> }
>> >>
>> >> -#define SHOW_FUNCTION_PER_GROUP(__VAR) \
>> >> +static int
>> >> +blkiocg_reset_write(struct cgroup *cgroup, struct cftype *cftype, u64 val)
>> >> +{
>> >> + struct blkio_cgroup *blkcg;
>> >> + struct blkio_group *blkg;
>> >> + struct hlist_node *n;
>> >> + struct blkio_group_stats *stats;
>> >> +
>> >> + blkcg = cgroup_to_blkio_cgroup(cgroup);
>> >> + spin_lock_irq(&blkcg->lock);
>> >> + hlist_for_each_entry(blkg, n, &blkcg->blkg_list, blkcg_node) {
>> >> + spin_lock(&blkg->stats_lock);
>> >> + stats = &blkg->stats;
>> >> + memset(stats, 0, sizeof(struct blkio_group_stats));
>> >> + spin_unlock(&blkg->stats_lock);
>> >> + }
>> >> + spin_unlock_irq(&blkcg->lock);
>> >> + return 0;
>> >> +}
>> >> +
>> >> +static void blkio_get_key_name(int type, dev_t dev, char *str, int chars_left)
>> >> +{
>> >> + snprintf(str, chars_left, "%u:%u", MAJOR(dev), MINOR(dev));
>> >> + chars_left -= strlen(str);
>> >> + if (chars_left <= 0) {
>> >> + printk(KERN_WARNING
>> >> + "Possibly incorrect cgroup stat display format");
>> >> + return;
>> >> + }
>> >> + switch (type) {
>> >> + case IO_READ:
>> >> + strlcat(str, " Read", chars_left);
>> >> + break;
>> >> + case IO_WRITE:
>> >> + strlcat(str, " Write", chars_left);
>> >> + break;
>> >> + case IO_SYNC:
>> >> + strlcat(str, " Sync", chars_left);
>> >> + break;
>> >> + case IO_ASYNC:
>> >> + strlcat(str, " Async", chars_left);
>> >> + break;
>> >> + case IO_TYPE_TOTAL:
>> >> + strlcat(str, " Total", chars_left);
>> >> + break;
>> >> + default:
>> >> + strlcat(str, " Invalid", chars_left);
>> >> + }
>> >> +}
>> >> +
>> >> +typedef uint64_t (get_var) (struct blkio_group *, int);
>> >> +
>> >> +static uint64_t blkio_get_typed_stat(struct blkio_group *blkg,
>> >> + struct cgroup_map_cb *cb, get_var *getvar, dev_t dev)
>> >> +{
>> >> + uint64_t disk_total;
>> >> + char key_str[MAX_KEY_LEN];
>> >> + int type;
>> >> +
>> >> + for (type = 0; type < IO_TYPE_TOTAL; type++) {
>> >> + blkio_get_key_name(type, dev, key_str, MAX_KEY_LEN);
>> >> + cb->fill(cb, key_str, getvar(blkg, type));
>> >> + }
>> >> + disk_total = getvar(blkg, IO_READ) + getvar(blkg, IO_WRITE);
>> >> + blkio_get_key_name(IO_TYPE_TOTAL, dev, key_str, MAX_KEY_LEN);
>> >> + cb->fill(cb, key_str, disk_total);
>> >> + return disk_total;
>> >> +}
>> >> +
>> >> +static uint64_t blkio_get_stat(struct blkio_group *blkg,
>> >> + struct cgroup_map_cb *cb, get_var *getvar, dev_t dev)
>> >> +{
>> >> + uint64_t var = getvar(blkg, 0);
>> >> + char str[10];
>> >> +
>> >> + snprintf(str, 10, "%u:%u", MAJOR(dev), MINOR(dev));
>> >> + cb->fill(cb, str, var);
>> >> + return var;
>> >> +}
>> >> +
>> >> +#define GET_STAT_INDEXED(__VAR) \
>> >> +uint64_t blkio_get_##__VAR##_stat(struct blkio_group *blkg, int type) \
>> >> +{ \
>> >> + return blkg->stats.__VAR[type]; \
>> >> +} \
>> >> +
>> >> +GET_STAT_INDEXED(io_service_bytes);
>> >> +GET_STAT_INDEXED(io_serviced);
>> >> +GET_STAT_INDEXED(io_service_time);
>> >> +GET_STAT_INDEXED(io_wait_time);
>> >> +#undef GET_STAT_INDEXED
>> >> +
>> >> +#define GET_STAT(__VAR) \
>> >> +uint64_t blkio_get_##__VAR##_stat(struct blkio_group *blkg, int dummy) \
>> >> +{ \
>> >> + return blkg->stats.__VAR; \
>> >> +}
>> >> +
>> >> +GET_STAT(time);
>> >> +GET_STAT(sectors);
>> >> +#ifdef CONFIG_DEBUG_BLK_CGROUP
>> >> +GET_STAT(dequeue);
>> >> +#endif
>> >> +#undef GET_STAT
>> >> +
>> >> +#define SHOW_FUNCTION_PER_GROUP(__VAR, get_stats, getvar, show_total) \
>> >> static int blkiocg_##__VAR##_read(struct cgroup *cgroup, \
>> >> - struct cftype *cftype, struct seq_file *m) \
>> >> + struct cftype *cftype, struct cgroup_map_cb *cb) \
>> >> { \
>> >> struct blkio_cgroup *blkcg; \
>> >> struct blkio_group *blkg; \
>> >> struct hlist_node *n; \
>> >> + uint64_t cgroup_total = 0; \
>> >> \
>> >> if (!cgroup_lock_live_group(cgroup)) \
>> >> return -ENODEV; \
>> >> @@ -184,19 +295,32 @@ static int blkiocg_##__VAR##_read(struct cgroup *cgroup, \
>> >> blkcg = cgroup_to_blkio_cgroup(cgroup); \
>> >> rcu_read_lock(); \
>> >> hlist_for_each_entry_rcu(blkg, n, &blkcg->blkg_list, blkcg_node) {\
>> >> - if (blkg->dev) \
>> >> - seq_printf(m, "%u:%u %lu\n", MAJOR(blkg->dev), \
>> >> - MINOR(blkg->dev), blkg->__VAR); \
>> >> + if (blkg->dev) { \
>> >> + spin_lock_irq(&blkg->stats_lock); \
>> >> + cgroup_total += get_stats(blkg, cb, getvar, \
>> >> + blkg->dev); \
>> >> + spin_unlock_irq(&blkg->stats_lock); \
>> >> + } \
>> >> } \
>> >> + if (show_total) \
>> >> + cb->fill(cb, "Total", cgroup_total); \
>> >> rcu_read_unlock(); \
>> >> cgroup_unlock(); \
>> >> return 0; \
>> >> }
>> >>
>> >> -SHOW_FUNCTION_PER_GROUP(time);
>> >> -SHOW_FUNCTION_PER_GROUP(sectors);
>> >> +SHOW_FUNCTION_PER_GROUP(time, blkio_get_stat, blkio_get_time_stat, 0);
>> >> +SHOW_FUNCTION_PER_GROUP(sectors, blkio_get_stat, blkio_get_sectors_stat, 0);
>> >> +SHOW_FUNCTION_PER_GROUP(io_service_bytes, blkio_get_typed_stat,
>> >> + blkio_get_io_service_bytes_stat, 1);
>> >> +SHOW_FUNCTION_PER_GROUP(io_serviced, blkio_get_typed_stat,
>> >> + blkio_get_io_serviced_stat, 1);
>> >> +SHOW_FUNCTION_PER_GROUP(io_service_time, blkio_get_typed_stat,
>> >> + blkio_get_io_service_time_stat, 1);
>> >> +SHOW_FUNCTION_PER_GROUP(io_wait_time, blkio_get_typed_stat,
>> >> + blkio_get_io_wait_time_stat, 1);
>> >> #ifdef CONFIG_DEBUG_BLK_CGROUP
>> >> -SHOW_FUNCTION_PER_GROUP(dequeue);
>> >> +SHOW_FUNCTION_PER_GROUP(dequeue, blkio_get_stat, blkio_get_dequeue_stat, 0);
>> >> #endif
>> >> #undef SHOW_FUNCTION_PER_GROUP
>> >>
>> >> @@ -204,7 +328,7 @@ SHOW_FUNCTION_PER_GROUP(dequeue);
>> >> void blkiocg_update_blkio_group_dequeue_stats(struct blkio_group *blkg,
>> >> unsigned long dequeue)
>> >> {
>> >> - blkg->dequeue += dequeue;
>> >> + blkg->stats.dequeue += dequeue;
>> >> }
>> >> EXPORT_SYMBOL_GPL(blkiocg_update_blkio_group_dequeue_stats);
>> >> #endif
>> >> @@ -217,16 +341,39 @@ struct cftype blkio_files[] = {
>> >> },
>> >> {
>> >> .name = "time",
>> >> - .read_seq_string = blkiocg_time_read,
>> >> + .read_map = blkiocg_time_read,
>> >> + .write_u64 = blkiocg_reset_write,
>> >> },
>> >> {
>> >> .name = "sectors",
>> >> - .read_seq_string = blkiocg_sectors_read,
>> >> + .read_map = blkiocg_sectors_read,
>> >> + .write_u64 = blkiocg_reset_write,
>> >> + },
>> >> + {
>> >> + .name = "io_service_bytes",
>> >> + .read_map = blkiocg_io_service_bytes_read,
>> >> + .write_u64 = blkiocg_reset_write,
>> >> + },
>> >> + {
>> >> + .name = "io_serviced",
>> >> + .read_map = blkiocg_io_serviced_read,
>> >> + .write_u64 = blkiocg_reset_write,
>> >> + },
>> >> + {
>> >> + .name = "io_service_time",
>> >> + .read_map = blkiocg_io_service_time_read,
>> >> + .write_u64 = blkiocg_reset_write,
>> >> + },
>> >> + {
>> >> + .name = "io_wait_time",
>> >> + .read_map = blkiocg_io_wait_time_read,
>> >> + .write_u64 = blkiocg_reset_write,
>> >> },
>> >> #ifdef CONFIG_DEBUG_BLK_CGROUP
>> >> {
>> >> .name = "dequeue",
>> >> - .read_seq_string = blkiocg_dequeue_read,
>> >> + .read_map = blkiocg_dequeue_read,
>> >> + .write_u64 = blkiocg_reset_write,
>> >> },
>> >> #endif
>> >> };
>> >> diff --git a/block/blk-cgroup.h b/block/blk-cgroup.h
>> >> index fe44517..e8600b0 100644
>> >> --- a/block/blk-cgroup.h
>> >> +++ b/block/blk-cgroup.h
>> >> @@ -23,6 +23,14 @@ extern struct cgroup_subsys blkio_subsys;
>> >> #define blkio_subsys_id blkio_subsys.subsys_id
>> >> #endif
>> >>
>> >> +enum io_type {
>> >> + IO_READ = 0,
>> >> + IO_WRITE,
>> >> + IO_SYNC,
>> >> + IO_ASYNC,
>> >> + IO_TYPE_TOTAL
>> >> +};
>> >> +
>> >> struct blkio_cgroup {
>> >> struct cgroup_subsys_state css;
>> >> unsigned int weight;
>> >> @@ -30,6 +38,23 @@ struct blkio_cgroup {
>> >> struct hlist_head blkg_list;
>> >> };
>> >>
>> >> +struct blkio_group_stats {
>> >> + /* total disk time and nr sectors dispatched by this group */
>> >> + uint64_t time;
>> >> + uint64_t sectors;
>> >> + /* Total disk time used by IOs in ns */
>> >> + uint64_t io_service_time[IO_TYPE_TOTAL];
>> >> + uint64_t io_service_bytes[IO_TYPE_TOTAL]; /* Total bytes transferred */
>> >> + /* Total IOs serviced, post merge */
>> >> + uint64_t io_serviced[IO_TYPE_TOTAL];
>> >> + /* Total time spent waiting in scheduler queue in ns */
>> >> + uint64_t io_wait_time[IO_TYPE_TOTAL];
>> >> +#ifdef CONFIG_DEBUG_BLK_CGROUP
>> >> + /* How many times this group has been removed from service tree */
>> >> + unsigned long dequeue;
>> >> +#endif
>> >> +};
>> >> +
>> >> struct blkio_group {
>> >> /* An rcu protected unique identifier for the group */
>> >> void *key;
>> >> @@ -38,15 +63,13 @@ struct blkio_group {
>> >> #ifdef CONFIG_DEBUG_BLK_CGROUP
>> >> /* Store cgroup path */
>> >> char path[128];
>> >> - /* How many times this group has been removed from service tree */
>> >> - unsigned long dequeue;
>> >> #endif
>> >> /* The device MKDEV(major, minor), this group has been created for */
>> >> - dev_t dev;
>> >> + dev_t dev;
>> >>
>> >> - /* total disk time and nr sectors dispatched by this group */
>> >> - unsigned long time;
>> >> - unsigned long sectors;
>> >> + /* Need to serialize the stats in the case of reset/update */
>> >> + spinlock_t stats_lock;
>> >> + struct blkio_group_stats stats;
>> >> };
>> >>
>> >> typedef void (blkio_unlink_group_fn) (void *key, struct blkio_group *blkg);
>> >> @@ -105,8 +128,8 @@ extern void blkiocg_add_blkio_group(struct blkio_cgroup *blkcg,
>> >> extern int blkiocg_del_blkio_group(struct blkio_group *blkg);
>> >> extern struct blkio_group *blkiocg_lookup_group(struct blkio_cgroup *blkcg,
>> >> void *key);
>> >> -void blkiocg_update_blkio_group_stats(struct blkio_group *blkg,
>> >> - unsigned long time);
>> >> +void blkiocg_update_timeslice_used(struct blkio_group *blkg,
>> >> + unsigned long time);
>> >> #else
>> >> struct cgroup;
>> >> static inline struct blkio_cgroup *
>> >> @@ -122,7 +145,7 @@ blkiocg_del_blkio_group(struct blkio_group *blkg) { return 0; }
>> >>
>> >> static inline struct blkio_group *
>> >> blkiocg_lookup_group(struct blkio_cgroup *blkcg, void *key) { return NULL; }
>> >> -static inline void blkiocg_update_blkio_group_stats(struct blkio_group *blkg,
>> >> +static inline void blkiocg_update_timeslice_used(struct blkio_group *blkg,
>> >> unsigned long time) {}
>> >> #endif
>> >> #endif /* _BLK_CGROUP_H */
>> >> diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
>> >> index c18e348..d91df9f 100644
>> >> --- a/block/cfq-iosched.c
>> >> +++ b/block/cfq-iosched.c
>> >> @@ -914,7 +914,7 @@ static void cfq_group_served(struct cfq_data *cfqd, struct cfq_group *cfqg,
>> >>
>> >> cfq_log_cfqg(cfqd, cfqg, "served: vt=%llu min_vt=%llu", cfqg->vdisktime,
>> >> st->min_vdisktime);
>> >> - blkiocg_update_blkio_group_stats(&cfqg->blkg, used_sl);
>> >> + blkiocg_update_timeslice_used(&cfqg->blkg, used_sl);
>> >> }
>> >>
>> >> #ifdef CONFIG_CFQ_GROUP_IOSCHED
>> >
>
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