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Message-ID: <p2maf41c7c41004051629tcec7cc63ud5285929177029f2@mail.gmail.com>
Date: Mon, 5 Apr 2010 16:29:06 -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 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.
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?
-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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