Messages in this thread | | | Date | Tue, 04 Sep 2012 22:12:49 +0800 | From | Tao Ma <> | Subject | Re: [PATCH V2] block/throttle: Add IO throttled information in blkio.throttle. |
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On 09/04/2012 09:35 PM, Vivek Goyal wrote: > On Fri, Aug 31, 2012 at 01:15:09PM +0800, Tao Ma wrote: > > [..] >> diff --git a/block/blk-throttle.c b/block/blk-throttle.c >> index 1588c2d..9317d71 100644 >> --- a/block/blk-throttle.c >> +++ b/block/blk-throttle.c >> @@ -46,6 +46,8 @@ struct tg_stats_cpu { >> struct blkg_rwstat service_bytes; >> /* total IOs serviced, post merge */ >> struct blkg_rwstat serviced; >> + /* total IOs queued, not submitted to the underlying device. */ >> + struct blkg_rwstat io_queued; >> }; > > Couple of questions. > > - blkg_rwstat is "unsigned" and io_queued can go negative too (Because > throttled bio can very well be dispatched from other cpu from a worker > thread). So is it a good idea to represent a negative number with > unsingned type? > > - As this stat is per cpu, a reader might very well see negative (or a > huge unsigned value) as number of io_queued. Not sure if that is acceptable. > How would user space come to know whether it is a valid value or not. I > thought per cpu stats are good for continuously increasing values but > not necessarily for values which can increase as well as decrease. You are right. So I should just use throtl_grp->nr_queued to display the total numbers of ios being throttled and I guess a rcu_read_lock should be enough for me to access that data.
Thanks for the review.
Thanks Tao
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