linux-kernel - Re: [PATCH v4 6/7] sched: add function nr_running_cpu to expose number of tasks running on cpu

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Date:	Mon, 14 Jul 2014 21:15:04 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
Cc:	Herbert Xu <herbert@...dor.apana.org.au>,
	"H. Peter Anvin" <hpa@...or.com>,
	"David S.Miller" <davem@...emloft.net>,
	Ingo Molnar <mingo@...nel.org>,
	Chandramouli Narayanan <mouli@...ux.intel.com>,
	Vinodh Gopal <vinodh.gopal@...el.com>,
	James Guilford <james.guilford@...el.com>,
	Wajdi Feghali <wajdi.k.feghali@...el.com>,
	Jussi Kivilinna <jussi.kivilinna@....fi>,
	linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 6/7] sched: add function nr_running_cpu to expose
 number of tasks running on cpu

On Mon, Jul 14, 2014 at 12:08:28PM -0700, Tim Chen wrote:
> On Mon, 2014-07-14 at 20:17 +0200, Peter Zijlstra wrote:

> > Your multi-buffer thing isn't generic either, it seems lmiited to sha1.
> 
> We actually have many other multi-buffer crypto algorithms already
> published for encryption and other IPSec usages.  So 
> multi-buffer algorithm is not just limited to SHA1.
> We hope to port those to the kernel crypto library eventually.
> http://www.intel.com/content/dam/www/public/us/en/documents/white-papers/fast-multi-buffer-ipsec-implementations-ia-processors-paper.pdf 

That's all nice and such; but the code as I've seen in these patches is
very much sha1 specific. The mb part isn't separated out.

> > It does not reuse padata, 
> padata tries to speed things up by parallelizing jobs to *multiple*
> cpus.  Whereas multi-buffer tries to speed things up by speeding things
> up by using multiple data lanes in SIMD register in a *single* cpu.
> These two usages are complementary but not the same.

And if its single cpu, wth do you need that nr_running thing for another
cpu for?

Also, this difference wasn't clear to me.

I still loathe all the async work, because it makes a mockery of
accounting etc.. but that's a story for another day I suppose :-(



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