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Message-ID: <x2zaf41c7c41004051516u6e0aee91ta68a542d366e0dcc@mail.gmail.com>
Date: Mon, 5 Apr 2010 15:16:35 -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] blkio: Add io controller stats like
On Mon, Apr 5, 2010 at 7:45 AM, Vivek Goyal <vgoyal@...hat.com> wrote:
> On Fri, Apr 02, 2010 at 01:53:30PM -0700, Divyesh Shah wrote:
>
> [..]
>> >> +#define GET_STAT_INDEXED(__VAR) \
>> >> +uint64_t 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, __CONV) \
>> >> +uint64_t get_##__VAR##_stat(struct blkio_group *blkg, int dummy) \
>> >> +{ \
>> >> + uint64_t data = blkg->stats.__VAR; \
>> >> + if (__CONV) \
>> >> + data = (uint64_t)jiffies_to_msecs(data) * NSEC_PER_MSEC;\
>> >> + return data; \
>> >> +}
>> >> +
>> >> +GET_STAT(time, 1);
>> >> +GET_STAT(sectors, 0);
>> >> +#ifdef CONFIG_DEBUG_BLK_CGROUP
>> >> +GET_STAT(dequeue, 0);
>> >> +#endif
>> >> +#undef GET_STAT
>> >> +
>> >
>> > I think now so many macros to define different kind of functions is
>> > becoming really confusing. How about creating a two dimensional stat
>> > array which is indexed by type of io stat like "io_service_time" and
>> > then indexed by sub io type that is "READ, WRITE, SYNC" etc. And we
>> > can define a single function to read all kind of stats.
>> >
>> > That way we will not have to define one GET_STAT_INDEXED() and GET_STAT()
>> > for each unindexed variable. If there are not multiple functions then,
>> > then everywhere we don't have to pass around a function pointer to read
>> > the variable stat and code should become much simpler. Example, code
>> > follows.
>> >
>> >
>> > enum stat_type {
>> > BLKIO_STAT_TIME
>> > BLKIO_STAT_SECTORS
>> > BLKIO_STAT_WAIT_TIME
>> > BLKIO_STAT_SERVICE_TIME
>> > }
>> >
>> > enum stat_sub_type {
>> > BLKIO_STAT_READ
>> > BLKIO_STAT_WRITE
>> > BLKIO_STAT_SYNC
>> > }
>> >
>> > blkio_get_stat_var(enum stat_type var, enum stat_sub_type var_type) {
>> >
>> > if (var == BLKIO_STAT_TIME)
>> > reutrn blkg->stat.time
>> >
>> > /* Same as above for sectors */
>> >
>> > return blkg->stat[var][var_type];
>> > }
>>
>> I'm not sure adding this level of complexity (2nd dimension for stats)
>> and the numerous if (..) statements (or switch) is warranted
>
> I think we need only two conditions to check. BLKIO_STAT_TIME and
> BLKIO_STAT_SECTROS. Rest of these fall into typed category and we
> don't have to check for tyeps.
>
>> when they
>> only apply for the get_stat() and get_typed_stat() functions. This
>> seems like a more complicated simplification :).
>
> I think this really is simplification. This also gets rid of all the
> function pointers you are passing around to differentiate between two
> types of stats. Also gets rid of special macros to generate one function
> each for one kind of stat. These dynamic macros make code hard to read
> and understand.
>
> Can you please try this two dimensional array for stats approach once.
> I belive your code will be much easier to read.
There are 2 conditions now but as I mentioned that this is one of 2-3
patchsets for adding stats. More stats will increase the special
casing. I do agree the macros aren't exactly easy to read. I'll try
your suggested approach next and post a patchset when I'm done.
>
>>
>> >
>> > Also all these get_* function needs to be static.
>> Done
>> >
>> >> +#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; \
>> >> + char disk_id[10]; \
>> >> \
>> >> 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); \
>> >> + snprintf(disk_id, 10, "%u:%u", MAJOR(blkg->dev),\
>> >> + MINOR(blkg->dev)); \
>> >> + cgroup_total += get_stats(blkg, cb, getvar, \
>> >> + disk_id); \
>> >> + 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, get_stat, get_time_stat, 0);
>> >> +SHOW_FUNCTION_PER_GROUP(sectors, get_stat, get_sectors_stat, 0);
>> >> +SHOW_FUNCTION_PER_GROUP(io_service_bytes, get_typed_stat,
>> >> + get_io_service_bytes_stat, 1);
>> >> +SHOW_FUNCTION_PER_GROUP(io_serviced, get_typed_stat, get_io_serviced_stat, 1);
>> >> +SHOW_FUNCTION_PER_GROUP(io_service_time, get_typed_stat,
>> >> + get_io_service_time_stat, 1);
>> >> +SHOW_FUNCTION_PER_GROUP(io_wait_time, get_typed_stat, get_io_wait_time_stat, 1);
>> >> #ifdef CONFIG_DEBUG_BLK_CGROUP
>> >> -SHOW_FUNCTION_PER_GROUP(dequeue);
>> >> +SHOW_FUNCTION_PER_GROUP(dequeue, get_stat, 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 +341,38 @@ 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,
>> >> },
>> >
>> > blkiocg_reset_write() is invoked if a user does some write on any of the
>> > above files. This will reset all the stats. So if I do echo x >
>> > blkio.time, I will see all other files being reset? I think this is
>> > little counter intutive.
>> >
>> > Either we need to reset only those specific stats (the file being written
>> > to) or may be we can provide a separate file "blkio.reset_stats" to reset
>> > all the stats?
>>
>> I added a note in the Documentation file that writing an int to any of
>> the stats should reset all. I don't get the point of introducing
>> another file for this and would want stats to be cleared all together
>> in order to have say io_service_time and io_serviced in sync, i.e.,
>> the io_service_time should always be the total service time for the
>> IOs accounted for in io_serviced.
>>
>
> I agree that reset should mean reset of all stats. It is a matter of
> whether to introduce a separate file or write to one file resets all the
> other files. Though I find writting to one file resetting the stats of
> other file un-intitutive, at the same time don't feel too excited about
> introducing a new file just for reset.
>
> Do we really need to introduce reset interface. Changing the ioscheduler to
> noop or deadline and then setting it back to cfq should reset the stats for
> all the cgroups.
>
> In fact we can probably get rid of per cgroup reset stats interface. We
> will then get rid of extra stat spin lock. If somebody wants to reset
> the stats, just change the ioscheduler.
> This will work until and unless somebody wants to reset the stats of one
> cgroup but not the other.
As mentioned on the other thread this is exactly what I find the main
use case of this interface. Once again, if you feel too strongly about
it we can have a separate reset_stats interface to make it more
intuitive.
>
> Thanks
> Vivek
>
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