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SubjectRe: [PATCH 0/3] dm-verity: optionally use tasklets in dm-verity
We've been tying to kill off task lets for about 15 years.  I don't
think adding new users will make you a whole lot of friends..

On Fri, Jul 22, 2022 at 09:38:20AM +0000, Nathan Huckleberry wrote:
> Using tasklets for disk verification can reduce IO latency. When there are
> accelerated hash instructions it is often better to compute the hash immediately
> using a tasklet rather than deferring verification to a work-queue. This
> reduces time spent waiting to schedule work-queue jobs, but requires spending
> slightly more time in interrupt context.
>
> A tasklet can only be used for verification if all the required hashes are
> already in the dm-bufio cache. If verification cannot be done in a tasklet, we
> fallback the existing work-queue implementation.
>
> To allow tasklets to query the dm-bufio cache, the dm-bufio code must not sleep.
> This patchset adds a flag to dm-bufio that disallows sleeping.
>
> The following shows a speed comparison of random reads on a dm-verity device.
> The dm-verity device uses a 1G ramdisk for data and a 1G ramdisk for hashes.
> One test was run using tasklets and one test was run using the existing
> work-queue solution. Both tests were run when the dm-bufio cache was hot. The
> tasklet implementation performs significantly better since there is no time
> waiting for work-queue jobs to be scheduled.
>
> # /data/fio /data/tasklet.fio | grep READ
> READ: bw=181MiB/s (190MB/s), 181MiB/s-181MiB/s (190MB/s-190MB/s), io=512MiB
> (537MB), run=2827-2827msec
> # /data/fio /data/workqueue.fio | grep READ
> READ: bw=23.6MiB/s (24.8MB/s), 23.6MiB/s-23.6MiB/s (24.8MB/s-24.8MB/s),
> io=512MiB (537MB), run=21688-21688msec
>
> Nathan Huckleberry (3):
> dm-bufio: Add flags for dm_bufio_client_create
> dm-bufio: Add DM_BUFIO_GET_CANT_SLEEP
> dm-verity: Add try_verify_in_tasklet
>
> drivers/md/dm-bufio.c | 29 +++++--
> drivers/md/dm-ebs-target.c | 3 +-
> drivers/md/dm-integrity.c | 2 +-
> drivers/md/dm-snap-persistent.c | 2 +-
> drivers/md/dm-verity-fec.c | 4 +-
> drivers/md/dm-verity-target.c | 87 ++++++++++++++++---
> drivers/md/dm-verity.h | 5 ++
> drivers/md/persistent-data/dm-block-manager.c | 3 +-
> include/linux/dm-bufio.h | 8 +-
> 9 files changed, 119 insertions(+), 24 deletions(-)
>
> --
> 2.37.1.359.gd136c6c3e2-goog
>
---end quoted text---

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