linux-kernel - Re: sched: Performance of Trade workload running inside VM

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

Message-ID: <20120218074127.GA9077@linux.vnet.ibm.com>
Date:	Sat, 18 Feb 2012 13:11:27 +0530
From:	Srivatsa Vaddagiri <vatsa@...ux.vnet.ibm.com>
To:	Peter Zijlstra <a.p.zijlstra@...llo.nl>
Cc:	mingo@...e.hu, pjt@...gle.com, efault@....de, venki@...gle.com,
	suresh.b.siddha@...el.com, linux-kernel@...r.kernel.org,
	" Nikunj A. Dadhania" <nikunj@...ux.vnet.ibm.com>
Subject: Re: sched: Performance of Trade workload running inside VM

* Peter Zijlstra <a.p.zijlstra@...llo.nl> [2012-02-15 18:45:02]:

> I'm still waiting for a problem description that isn't a book.
> 
> What does the load-balancer do,

select_idle_sibling() tries finding a core (sched group) which is fully idle
failing which will let task wakeup on prev_cpu.

> why is it wrong,

Take this scenario. wakeup source for task is cpu0 while its prev_cpu is
cpu7 (which is in another cache domain).

		cache_dom0		cache_dom1
		(0, 1) (2, 3)		(4, 5) (6, 7)
nr_running->	 1  1   1  1     	 0, 1   1, 2

In this case we let task wakeup on cpu7, resulting in it incurring some
wait time before being scheduled. A better choice would have been cpu4 (whose
core is partially idle) or in general any other less-loaded cpu which is in same
cache domain?

> why does your patch sort it etc.

The patch does result in a hunt for "least" busy cpu when the target cpu
returned by select_idle_sibling() is not idle - thus resulting in better
scheduling latencies for the task (and in turn better benchmark scores).

Another variant of the patch could be to have select_idle_sibling() look
for any idle cpu that is in same cache domain (rather than looking for a
whole group of cpus to be idle)?

- vatsa

--
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/