Messages in this thread | | | Subject | Re: [PATCH -next v4 4/4] blk-throttle: fix io hung due to config updates | From | Yu Kuai <> | Date | Tue, 24 May 2022 19:47:49 +0800 |
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在 2022/05/24 17:59, Michal Koutný 写道: > On Mon, May 23, 2022 at 04:26:33PM +0800, Yu Kuai <yukuai3@huawei.com> wrote: >> Fix the problem by respecting the time that throttled bio aready waited. >> In order to do that, add new fields to record how many bytes/io already >> waited, and use it to calculate wait time for throttled bio under new >> configuration. > > This new approach is correctly conserving the bandwidth upon changes. > (Looking and BPS paths.) > >> >> Some simple test: >> 1) >> cd /sys/fs/cgroup/blkio/ >> echo $$ > cgroup.procs >> echo "8:0 2048" > blkio.throttle.write_bps_device >> { >> sleep 3 >> echo "8:0 1024" > blkio.throttle.write_bps_device >> } & >> sleep 1 >> dd if=/dev/zero of=/dev/sda bs=8k count=1 oflag=direct >> >> 2) >> cd /sys/fs/cgroup/blkio/ >> echo $$ > cgroup.procs >> echo "8:0 1024" > blkio.throttle.write_bps_device >> { >> sleep 5 >> echo "8:0 2048" > blkio.throttle.write_bps_device >> } & >> sleep 1 >> dd if=/dev/zero of=/dev/sda bs=8k count=1 oflag=direct >> > > It's interesting that you're getting these numbers (w/patch) > >> test results: io finish time >> before this patch with this patch >> 1) 10s 6s >> 2) 8s 6s > > wait := (disp + bio - Δt*l_old) / l_new > > 1) > wait = (0k + 8k - 3s*2k/s) / 1k/s = 2s -> i.e. 5s absolute > > 2) > wait = (0k + 8k - 5s*1k/s) / 2k/s = 2.5s -> i.e. 6.5s absolute > > Are you numbers noisy+rounded or do I still mis anything? Hi, Michal
The way of your caculation is right, however, it seems like you missed that io is dispatched after 1s:
sleep 1 -> here dd if=/dev/zero of=/dev/sda bs=8k count=1 oflag=direct > > (Also isn't it worth having this more permanent in tools/testing/selftest?) > >> +static void tg_update_skipped(struct throtl_grp *tg) >> +{ >> + if (tg->service_queue.nr_queued[READ]) >> + __tg_update_skipped(tg, READ); >> + if (tg->service_queue.nr_queued[WRITE]) >> + __tg_update_skipped(tg, WRITE); > > On one hand, the callers of tg_update_skipped() know whether R/W limit > is changed, so only the respective variant could be called. > On the other hand, this conditions look implied by tg->flags & > THROTL_TG_PENDING. > (Just noting, it's likely still not possibly to pass the skipped value > only via stack.) > > >> @@ -115,6 +115,10 @@ struct throtl_grp { >> uint64_t bytes_disp[2]; >> /* Number of bio's dispatched in current slice */ >> unsigned int io_disp[2]; >> + /* Number of bytes will be skipped in current slice */ >> + uint64_t bytes_skipped[2]; >> + /* Number of bio's will be skipped in current slice */ >> + unsigned int io_skipped[2]; > > Please add a comment these fields exists to facilitate config updates > (the bytes to be skipped is sort of obvious from the name :-). Ok, will do that in next iteration.
Thanks, Kuai
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