linux-kernel - Re: [PATCH v2 1/3] block/blk-throttle: Fix throttle slice time for SSDs

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Message-Id: <2d827b93-9ffa-4767-8409-88460e64a407@fnnas.com>
Date: Sat, 15 Nov 2025 23:51:27 +0800
From: "Yu Kuai" <yukuai@...as.com>
To: "Khazhismel Kumykov" <khazhy@...omium.org>, "Tejun Heo" <tj@...nel.org>, 
	"Josef Bacik" <josef@...icpanda.com>, "Jens Axboe" <axboe@...nel.dk>
Cc: <cgroups@...r.kernel.org>, <linux-block@...r.kernel.org>, 
	<linux-kernel@...r.kernel.org>, "Guenter Roeck" <linux@...ck-us.net>, 
	"Yu Kuai" <yukuai@...nel.org>, "Khazhismel Kumykov" <khazhy@...gle.com>
Subject: Re: [PATCH v2 1/3] block/blk-throttle: Fix throttle slice time for SSDs

在 2025/11/15 7:54, Khazhismel Kumykov 写道:
> From: Guenter Roeck<linux@...ck-us.net>
>
> Commit d61fcfa4bb18 ("blk-throttle: choose a small throtl_slice for SSD")
> introduced device type specific throttle slices if BLK_DEV_THROTTLING_LOW
> was enabled. Commit bf20ab538c81 ("blk-throttle: remove
> CONFIG_BLK_DEV_THROTTLING_LOW") removed support for BLK_DEV_THROTTLING_LOW,
> but left the device type specific throttle slices in place. This
> effectively changed throttling behavior on systems with SSD which now use
> a different and non-configurable slice time compared to non-SSD devices.
> Practical impact is that throughput tests with low configured throttle
> values (65536 bps) experience less than expected throughput on SSDs,
> presumably due to rounding errors associated with the small throttle slice
> time used for those devices. The same tests pass when setting the throttle
> values to 65536 * 4 = 262144 bps.
>
> The original code sets the throttle slice time to DFL_THROTL_SLICE_HD if
> CONFIG_BLK_DEV_THROTTLING_LOW is disabled. Restore that code to fix the
> problem. With that, DFL_THROTL_SLICE_SSD is no longer necessary. Revert to
> the original code and re-introduce DFL_THROTL_SLICE to replace both
> DFL_THROTL_SLICE_HD and DFL_THROTL_SLICE_SSD. This effectively reverts
> commit d61fcfa4bb18 ("blk-throttle: choose a small throtl_slice for SSD").
>
> While at it, also remove MAX_THROTL_SLICE since it is not used anymore.
>
> Fixes: bf20ab538c81 ("blk-throttle: remove CONFIG_BLK_DEV_THROTTLING_LOW")
> Cc: Yu Kuai<yukuai@...nel.org>
> Cc: Tejun Heo<tj@...nel.org>
> Signed-off-by: Guenter Roeck<linux@...ck-us.net>
> Signed-off-by: Khazhismel Kumykov<khazhy@...gle.com>
> ---
>   block/blk-throttle.c | 9 ++-------
>   1 file changed, 2 insertions(+), 7 deletions(-)

LGTM
Reviewed-by: Yu Kuai <yukuai@...as.com>

-- 
Thanks
Kuai