Messages in this thread | | | From | Divyesh Shah <> | Date | Mon, 5 Apr 2010 15:06:31 -0700 | Subject | Re: [PATCH 3/3] blkio: Increment the blkio cgroup stats for real now |
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On Mon, Apr 5, 2010 at 10:29 AM, Vivek Goyal <vgoyal@redhat.com> wrote: > On Mon, Apr 05, 2010 at 09:53:25AM -0700, Divyesh Shah wrote: >> On Mon, Apr 5, 2010 at 8:12 AM, Vivek Goyal <vgoyal@redhat.com> wrote: >> > On Fri, Apr 02, 2010 at 04:36:34PM -0700, Divyesh Shah wrote: >> >> On Fri, Apr 2, 2010 at 12:10 PM, Vivek Goyal <vgoyal@redhat.com> wrote: >> >> > On Thu, Apr 01, 2010 at 03:01:41PM -0700, Divyesh Shah wrote: >> >> >> We also add start_time_ns and io_start_time_ns fields to struct request >> >> >> here to record the time when a request is created and when it is >> >> >> dispatched to device. We use ns uints here as ms and jiffies are >> >> >> not very useful for non-rotational media. >> >> >> >> >> >> Signed-off-by: Divyesh Shah<dpshah@google.com> >> >> >> --- >> >> >> >> >> >> block/blk-cgroup.c | 60 ++++++++++++++++++++++++++++++++++++++++++++++-- >> >> >> block/blk-cgroup.h | 14 +++++++++-- >> >> >> block/blk-core.c | 6 +++-- >> >> >> block/cfq-iosched.c | 4 ++- >> >> >> include/linux/blkdev.h | 20 +++++++++++++++- >> >> >> 5 files changed, 95 insertions(+), 9 deletions(-) >> >> >> >> >> >> diff --git a/block/blk-cgroup.c b/block/blk-cgroup.c >> >> >> index ad6843f..9af7257 100644 >> >> >> --- a/block/blk-cgroup.c >> >> >> +++ b/block/blk-cgroup.c >> >> >> @@ -15,6 +15,7 @@ >> >> >> #include <linux/kdev_t.h> >> >> >> #include <linux/module.h> >> >> >> #include <linux/err.h> >> >> >> +#include <linux/blkdev.h> >> >> >> #include "blk-cgroup.h" >> >> >> >> >> >> static DEFINE_SPINLOCK(blkio_list_lock); >> >> >> @@ -55,6 +56,26 @@ struct blkio_cgroup *cgroup_to_blkio_cgroup(struct cgroup *cgroup) >> >> >> } >> >> >> EXPORT_SYMBOL_GPL(cgroup_to_blkio_cgroup); >> >> >> >> >> >> +/* >> >> >> + * Add to the appropriate stat variable depending on the request type. >> >> >> + * This should be called with the blkg->stats_lock held. >> >> >> + */ >> >> >> +void io_add_stat(uint64_t *stat, uint64_t add, unsigned int flags) >> >> >> +{ >> >> >> + if (flags & REQ_RW) >> >> >> + stat[IO_WRITE] += add; >> >> >> + else >> >> >> + stat[IO_READ] += add; >> >> >> + /* >> >> >> + * Everywhere in the block layer, an IO is treated as sync if it is a >> >> >> + * read or a SYNC write. We follow the same norm. >> >> >> + */ >> >> >> + if (!(flags & REQ_RW) || flags & REQ_RW_SYNC) >> >> >> + stat[IO_SYNC] += add; >> >> >> + else >> >> >> + stat[IO_ASYNC] += add; >> >> >> +} >> >> >> + >> >> > >> >> > Hi Divyesh, >> >> > >> >> > Can we have any request based information limited to cfq and not put that >> >> > in blkio-cgroup. The reason being that I am expecting that some kind of >> >> > max bw policy interface will not necessarily be implemented at CFQ >> >> > level. We might have to implement it at higher level so that it can >> >> > work with all dm/md devices. If that's the case, then it might very well >> >> > be either a bio based interface also. >> >> > >> >> > So just keeping that possibility in mind, can we keep blk-cgroup as >> >> > generic as possible and not necessarily make it dependent on "struct >> >> > request". >> >> >> >> Ok. I do understand the motivation for keeping the request related >> >> info out of blk-cgroup. Everything except the rq->cmd_flags can be >> >> easily done away with. Maybe I'll need to have CFQ send the sync and >> >> direction bits as args to the functions that need it. Not ideal coz >> >> we'll have functions with many args but I guess its not that bad too. >> >> >> >> > >> >> > If you implement, two dimensional arrays for stats then we can have >> >> > following function. >> >> > >> >> > blkio_add_stat(enum stat_type var enum stat_sub_type var_type, u64 val) >> >> >> >> I would want to avoid calls like these from CFQ into the blkcg code >> >> because many CFQ events trigger update for multiple stats (you'll see >> >> more with stats in later patchsets) and doing these calls >> >> independently for each stat would mean that we would also need to grab >> >> the stats_lock multiple times when we could've avoided that. >> > >> > I understand the need to club the updates and reduce the need of taking >> > stats_lock multiple times. I was thinking of any of following. >> > >> > - Get rid of reset interface per cgroup. Rely on changing ioscheduler on >> > request queue and that will get rid of stats_lock entirely. >> >> This takes away the ability to reset stats at will which is very >> useful when debugging and for testing IO controller. >> > > What do you mean by "reset stats at will"? You can change ioscheduler at > will and reset stats? The only possible issue I could think of is that only > admin can change the ioscheduler in providing per cgroup interface, one can > give write permission to indiviaul user and allow users to reset stats.
I should've said reset stats for a given cgroup at will. This is mostly needed when debugging and for automated tests where we're testing multiple cgroups and/or IO controller behavior between different workloads (sync readers, buffered writers, sync_writers, directIO read/write, etc). Resetting cgroup stats is something we use regularly and depend on. If you feel very strongly about this being counter-intuitive I can add a reset_stats file and make the other stats read-only.
> I am not sure in practice why would you allow a user to reset stats. > Especially if somebody's accounting software is based on these stats. > >> > - Can we use a function blkio_add_stat() with variable number of arguments >> > so that more than one stat can be updated in a single call? >> >> I really don't like this at all. >> >> > If you have other ideas to implement it without assuming "struct rq" in >> > blk-cgroup, please do that. >> >> I've already got rid of any rq assumptions in blk-cgroup. The only >> place where we're using rq is for rq_start_time_ns() and >> rq_io-start_time_ns() functions but they are not used by the >> blk-cgroup code directly (only CFQ uses them). For another user of >> io-controller, we can implement a bio based functions. > > Ok, you have made blkg->stats_lock visible to cfq. That's fine too.
By visible you mean accessible through cfqg->blkg, right? However, I don't intend to use it anywhere in cfq code.
> Can you rename io_add_stat to blkio_add_stat. I think in V2 also, it is > still io_add_stat.
Sorry I missed that one. Will do in v3. > > Vivek > -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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