On Mon, May 23, 2022 at 04:26:33PM +0800, Yu Kuai <yukuai3@xxxxxxxxxx> 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?
(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 :-).
Thanks,
Michal
