linux-kernel - Re: workqueue thing

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]

Date:	Wed, 23 Dec 2009 07:02:29 +0100
From:	Ingo Molnar <mingo@...e.hu>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Tejun Heo <tj@...nel.org>, Peter Zijlstra <peterz@...radead.org>,
	awalls@...ix.net, linux-kernel@...r.kernel.org, jeff@...zik.org,
	akpm@...ux-foundation.org, jens.axboe@...cle.com,
	rusty@...tcorp.com.au, cl@...ux-foundation.org,
	dhowells@...hat.com, arjan@...ux.intel.com, avi@...hat.com,
	johannes@...solutions.net, andi@...stfloor.org
Subject: Re: workqueue thing


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> Workqueues generally aren't about heavy CPU usage, although some workqueue 
> usage has scalability issues. And the most common scalability problem is not 
> "I need more than one CPU", but often "I need to run even though another 
> workqueue entry is blocked on IO" - iow, it's not about lacking CPU power, 
> it's about in-fighting with other workqueue users.
> 
> That said, if we can improve on this further, I'd be all for it. I'd love to 
> have some generic async model that really works. So far, our async models 
> have tended to not really work out well, whether they be softirq's or kernel 
> threads (many of the same issues: some subsystems start tons of kernel 
> threads just because one kernel thread blocks, not because you need 
> multi-processor CPU usage per se). And AIO/threadlets never got anywhere etc 
> etc.

Not from lack of trying though ;-)

One key thing i havent seen in this discussion are actual measurements. I 
think a lot could be decided by simply testing this patch-set, by looking at 
the hard numbers: how much faster (or slower) did a particular key workload 
get before/after these patches.

Likewise, if there's a reduction in complexity, that is a tangible metric as 
well: lets do a few conversions as part of the patch-set and see how much 
simpler things have become as a result of it.

We really are not forced to the space of Gedankenexperiments here.

	Ingo
--
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/