linux-kernel - [RFC,PATCH] cfq-iosched: improve async queue ramp up formula

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [thread-next>] [day] [month] [year] [list]

Message-Id: <200911261710.40719.czoccolo@gmail.com>
Date:	Thu, 26 Nov 2009 17:10:39 +0100
From:	Corrado Zoccolo <czoccolo@...il.com>
To:	"Linux-Kernel" <linux-kernel@...r.kernel.org>,
	Jens Axboe <jens.axboe@...cle.com>,
	Jeff Moyer <jmoyer@...hat.com>,
	Vivek Goyal <vgoyal@...hat.com>, mel@....ul.ie, efault@....de
Subject: [RFC,PATCH] cfq-iosched: improve async queue ramp up formula

The introduction of ramp-up formula for async queue depths has
slowed down dirty page reclaim, by reducing async write performance.
This patch improves the formula by considering the remaining slice.

The new formula will allow more dispatches at the beginning of the
slice, reducing them at the end.
This will ensure that we achieve good throughput, without the risk of
overrunning the allotted timeslice.

The threshold is automatically increased when sync I/O is not
intermingled with async, in accordance with the previous incarnation of
the formula.

Signed-off-by: Corrado Zoccolo <czoccolo@...il.com>
---
 block/cfq-iosched.c |   24 ++++++++++++++++++------
 1 files changed, 18 insertions(+), 6 deletions(-)

diff --git a/block/cfq-iosched.c b/block/cfq-iosched.c
index a5de31f..799782d 100644
--- a/block/cfq-iosched.c
+++ b/block/cfq-iosched.c
@@ -1633,12 +1633,24 @@ static bool cfq_may_dispatch(struct cfq_data *cfqd, struct cfq_queue *cfqq)
 	 * based on the last sync IO we serviced
 	 */
 	if (!cfq_cfqq_sync(cfqq) && cfqd->cfq_latency) {
-		unsigned long last_sync = jiffies - cfqd->last_end_sync_rq;
-		unsigned int depth;
-
-		depth = last_sync / cfqd->cfq_slice[1];
-		if (!depth && !cfqq->dispatched)
-			depth = 1;
+		unsigned long now = jiffies;
+		unsigned long last_sync = now - cfqd->last_end_sync_rq;
+		unsigned int depth = 1;
+		if (cfqq->slice_end > now) {
+			unsigned int num,den;
+			/*
+			 * (cfqq->slice_end - now) / cfqd->cfq_slice_idle
+			 * approximates the number of requests that can be
+			 * dispatched before our slice ends
+			 * last_sync/cfq_slice[1] gives a boost when no
+			 * concurrent sync activity is expected
+			 */
+			num = last_sync          * (cfqq->slice_end - now);
+			den = cfqd->cfq_slice[1] * cfqd->cfq_slice_idle;
+			if (!den)
+				den++;
+			depth += num / den;
+		}
 		if (depth < max_dispatch)
 			max_dispatch = depth;
 	}
-- 
1.6.2.5


--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/