linux-kernel - [PATCH RFC] Optimize semtimedop

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: <1271098163-3663-1-git-send-email-chris.mason@oracle.com>
Date:	Mon, 12 Apr 2010 14:49:21 -0400
From:	Chris Mason <chris.mason@...cle.com>
To:	chris.mason@...cle.com, zach.brown@...cle.com,
	jens.axboe@...cle.com, linux-kernel@...r.kernel.org,
	Nick Piggin <npiggin@...e.de>,
	Manfred Spraul <manfred@...orfullife.com>
Subject: [PATCH RFC] Optimize semtimedop

We've been poking around in semtimedop for a while now, mostly because
it is consistently showing up at the top of the CPU profiles for benchmarking
runs on big numa systems.  The biggest problem seems to be the IPC lock, and
the fact that we hold it for a long time while we loop over different lists and
try to do semaphore operations.

Zach Brown came up with a set of patches a while ago that switched away from
the global pending list, and semtimedop was recently optimized for the
single sop case by Nick and Manfred.

This patch series tries to build on ideas from all of these patches.  The
list of pending semaphore operations is pushed down to the individual
semaphore and the locking is also pushed down into the semaphore.  The
result is much faster with my micro benchmark:

http://oss.oracle.com/~mason/sembench.c

It more than doubles the total number of post/wait cycles the benchmark
is able to get in 30s.  Before this patch, semtimedop scored about the
same as futexes for the post/wait cycles, and so now it is 2x faster.

I did run this code through all of the ltp ipc tests, and later this week I
hope to get a full tpc database benchmark on it.

--
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/