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Fri, 11 Apr 2025 11:02:10 -0400 X-MC-Unique: ocm27zhmOLq00i6B3p7utA-1 X-Mimecast-MFC-AGG-ID: ocm27zhmOLq00i6B3p7utA_1744383729 Received: from mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com [10.30.177.111]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (2048 bits) server-digest SHA256) (No client certificate requested) by mx-prod-mc-02.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 17B7619560AD; Fri, 11 Apr 2025 15:02:08 +0000 (UTC) Received: from fedora (unknown [10.72.116.17]) by mx-prod-int-08.mail-002.prod.us-west-2.aws.redhat.com (Postfix) with ESMTPS id 5C9791801A69; Fri, 11 Apr 2025 15:02:01 +0000 (UTC) Date: Fri, 11 Apr 2025 23:01:56 +0800 From: Ming Lei To: Yu Kuai Cc: Jens Axboe , linux-block@vger.kernel.org, Tejun Heo , Josef Bacik , "yukuai (C)" , WoZ1zh1 Subject: Re: [PATCH 3/3] blk-throttle: carry over directly Message-ID: References: <20250305043123.3938491-1-ming.lei@redhat.com> <20250305043123.3938491-4-ming.lei@redhat.com> <14e6c54f-d0d9-0122-1e47-c8a56adbd5db@huaweicloud.com> Precedence: bulk X-Mailing-List: linux-block@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <14e6c54f-d0d9-0122-1e47-c8a56adbd5db@huaweicloud.com> X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.111 On Fri, Apr 11, 2025 at 10:53:12AM +0800, Yu Kuai wrote: > Hi, Ming > > 在 2025/03/05 12:31, Ming Lei 写道: > > Now ->carryover_bytes[] and ->carryover_ios[] only covers limit/config > > update. > > > > Actually the carryover bytes/ios can be carried to ->bytes_disp[] and > > ->io_disp[] directly, since the carryover is one-shot thing and only valid > > in current slice. > > > > Then we can remove the two fields and simplify code much. > > > > Type of ->bytes_disp[] and ->io_disp[] has to change as signed because the > > two fields may become negative when updating limits or config, but both are > > big enough for holding bytes/ios dispatched in single slice > > > > Cc: Tejun Heo > > Cc: Josef Bacik > > Cc: Yu Kuai > > Signed-off-by: Ming Lei > > --- > > block/blk-throttle.c | 49 +++++++++++++++++++------------------------- > > block/blk-throttle.h | 4 ++-- > > 2 files changed, 23 insertions(+), 30 deletions(-) > > > > diff --git a/block/blk-throttle.c b/block/blk-throttle.c > > index 7271aee94faf..91dab43c65ab 100644 > > --- a/block/blk-throttle.c > > +++ b/block/blk-throttle.c > > @@ -478,8 +478,6 @@ static inline void throtl_start_new_slice_with_credit(struct throtl_grp *tg, > > { > > tg->bytes_disp[rw] = 0; > > tg->io_disp[rw] = 0; > > - tg->carryover_bytes[rw] = 0; > > - tg->carryover_ios[rw] = 0; > > /* > > * Previous slice has expired. We must have trimmed it after last > > @@ -498,16 +496,14 @@ static inline void throtl_start_new_slice_with_credit(struct throtl_grp *tg, > > } > > static inline void throtl_start_new_slice(struct throtl_grp *tg, bool rw, > > - bool clear_carryover) > > + bool clear) > > { > > - tg->bytes_disp[rw] = 0; > > - tg->io_disp[rw] = 0; > > + if (clear) { > > + tg->bytes_disp[rw] = 0; > > + tg->io_disp[rw] = 0; > > + } > > tg->slice_start[rw] = jiffies; > > tg->slice_end[rw] = jiffies + tg->td->throtl_slice; > > - if (clear_carryover) { > > - tg->carryover_bytes[rw] = 0; > > - tg->carryover_ios[rw] = 0; > > - } > > throtl_log(&tg->service_queue, > > "[%c] new slice start=%lu end=%lu jiffies=%lu", > > @@ -617,20 +613,16 @@ static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw) > > */ > > time_elapsed -= tg->td->throtl_slice; > > bytes_trim = calculate_bytes_allowed(tg_bps_limit(tg, rw), > > - time_elapsed) + > > - tg->carryover_bytes[rw]; > > - io_trim = calculate_io_allowed(tg_iops_limit(tg, rw), time_elapsed) + > > - tg->carryover_ios[rw]; > > + time_elapsed); > > + io_trim = calculate_io_allowed(tg_iops_limit(tg, rw), time_elapsed); > > if (bytes_trim <= 0 && io_trim <= 0) > > return; > > - tg->carryover_bytes[rw] = 0; > > if ((long long)tg->bytes_disp[rw] >= bytes_trim) > > tg->bytes_disp[rw] -= bytes_trim; > > else > > tg->bytes_disp[rw] = 0; > > - tg->carryover_ios[rw] = 0; > > if ((int)tg->io_disp[rw] >= io_trim) > > tg->io_disp[rw] -= io_trim; > > else > > @@ -645,7 +637,8 @@ static inline void throtl_trim_slice(struct throtl_grp *tg, bool rw) > > jiffies); > > } > > -static void __tg_update_carryover(struct throtl_grp *tg, bool rw) > > +static void __tg_update_carryover(struct throtl_grp *tg, bool rw, > > + long long *bytes, int *ios) > > { > > unsigned long jiffy_elapsed = jiffies - tg->slice_start[rw]; > > u64 bps_limit = tg_bps_limit(tg, rw); > > @@ -658,26 +651,28 @@ static void __tg_update_carryover(struct throtl_grp *tg, bool rw) > > * configuration. > > */ > > if (bps_limit != U64_MAX) > > - tg->carryover_bytes[rw] += > > - calculate_bytes_allowed(bps_limit, jiffy_elapsed) - > > + *bytes = calculate_bytes_allowed(bps_limit, jiffy_elapsed) - > > tg->bytes_disp[rw]; > > if (iops_limit != UINT_MAX) > > - tg->carryover_ios[rw] += > > - calculate_io_allowed(iops_limit, jiffy_elapsed) - > > + *ios = calculate_io_allowed(iops_limit, jiffy_elapsed) - > > tg->io_disp[rw]; > > + tg->bytes_disp[rw] -= *bytes; > > + tg->io_disp[rw] -= *ios; > > This patch is applied before I get a chance to review. :( I think the > above update should be: oops, your review period takes too long(> 1 month), :-( > > tg->bytes_disp[rw] = -*bytes; > tg->io_disp[rw] = -*ios; I think the above is wrong since it simply override the existed dispatched bytes/ios. The calculation can be understood from two ways: 1) delta = calculate_bytes_allowed(bps_limit, jiffy_elapsed) - tg->bytes_disp[rw]; `delta` represents difference between theoretical and actual dispatch bytes. If `delta` > 0, it means we dispatch too less in past, and we have to subtract `delta` from ->bytes_disp, so that in future we can dispatch more. Similar with 'delta < 0'. 2) from consumer viewpoint: tg_within_bps_limit(): patched ... bytes_allowed = calculate_bytes_allowed(bps_limit, jiffy_elapsed_rnd); if (bytes_allowed > 0 && tg->bytes_disp[rw] + bio_size <= bytes_allowed) ... tg_within_bps_limit(): before patched ... bytes_allowed = calculate_bytes_allowed(bps_limit, jiffy_elapsed_rnd) + tg->carryover_bytes[rw]; if (bytes_allowed > 0 && tg->bytes_disp[rw] + bio_size <= bytes_allowed) ... So if `delta` is subtracted from `bytes_allowed` in patched code, we should subtract same bytes from ->byte_disp[] side for maintaining the relation. > > Otherwise, the result is actually (2 * disp - allowed), which might be a > huge value, causing long dealy for the next dispatch. > > This is what the old carryover fileds do, above change will work, but > look wried. As I explained, the patched code follows the original carryover calculation, and it passes all throt blktests. Or do you have test case broken by this patch? Thanks. Ming