From: Jason Low <jason.low2@hp.com>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Tim Chen <tim.c.chen@linux.intel.com>,
Paul Turner <pjt@google.com>, Ingo Molnar <mingo@kernel.org>,
Ben Segall <bsegall@google.com>,
LKML <linux-kernel@vger.kernel.org>,
jason.low2@hp.com
Subject: Re: [PATCH v2] sched: Reduce contention in update_cfs_rq_blocked_load
Date: Tue, 02 Sep 2014 00:41:24 -0700 [thread overview]
Message-ID: <1409643684.19197.15.camel@j-VirtualBox> (raw)
In-Reply-To: <20140901125505.GK27892@worktop.ger.corp.intel.com>
On Mon, 2014-09-01 at 14:55 +0200, Peter Zijlstra wrote:
> But yes, unbounded errors here are a problem, sure relaxing the updates
> makes things go fast, they also make things go skew.
Okay. In that case, would you like to take our original patch which
avoids unnecessary updates?
-----
Subject: [PATCH] sched: Reduce contention in update_cfs_rq_blocked_load
When running workloads on 2+ socket systems, based on perf profiles, the
update_cfs_rq_blocked_load function often shows up as taking up a
noticeable % of run time.
Much of the contention is in __update_cfs_rq_tg_load_contrib when we
update the tg load contribution stats. However, it turns out that in many
cases, they don't need to be updated and "tg_contrib" is 0.
This patch adds a check in __update_cfs_rq_tg_load_contrib to skip updating
tg load contribution stats when nothing needs to be updated. This reduces the
cacheline contention that would be unnecessary.
Cc: Yuyang Du <yuyang.du@intel.com>
Cc: Aswin Chandramouleeswaran <aswin@hp.com>
Cc: Chegu Vinod <chegu_vinod@hp.com>
Cc: Scott J Norton <scott.norton@hp.com>
Reviewed-by: Ben Segall <bsegall@google.com>
Reviewed-by: Waiman Long <Waiman.Long@hp.com>
Signed-off-by: Jason Low <jason.low2@hp.com>
---
kernel/sched/fair.c | 3 +++
1 files changed, 3 insertions(+), 0 deletions(-)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index d3427a8..45e346c 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -2382,6 +2382,9 @@ static inline void __update_cfs_rq_tg_load_contrib(struct cfs_rq *cfs_rq,
tg_contrib = cfs_rq->runnable_load_avg + cfs_rq->blocked_load_avg;
tg_contrib -= cfs_rq->tg_load_contrib;
+ if (!tg_contrib)
+ return;
+
if (force_update || abs(tg_contrib) > cfs_rq->tg_load_contrib / 8) {
atomic_long_add(tg_contrib, &tg->load_avg);
cfs_rq->tg_load_contrib += tg_contrib;
--
1.7.1
next prev parent reply other threads:[~2014-09-02 7:41 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-08-26 23:11 [PATCH v2] sched: Reduce contention in update_cfs_rq_blocked_load Jason Low
2014-08-26 23:24 ` Paul Turner
2014-08-27 17:34 ` Jason Low
2014-08-27 23:32 ` Tim Chen
2014-08-28 19:46 ` Jason Low
2014-09-01 12:55 ` Peter Zijlstra
2014-09-02 7:41 ` Jason Low [this message]
2014-09-03 11:32 ` Peter Zijlstra
2014-09-09 14:52 ` [tip:sched/core] sched: Reduce contention in update_cfs_rq_blocked_load() tip-bot for Jason Low
2014-08-27 19:18 ` [PATCH RESULT] sched: Rewrite per entity runnable load average tracking v5 Yuyang Du
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