linux-kernel - Re: [PATCH v3 0/7] x86: Rewrite switch

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Message-ID: <20160817051650.GA1581@gondor.apana.org.au>
Date:	Wed, 17 Aug 2016 13:16:50 +0800
From:	Herbert Xu <herbert@...dor.apana.org.au>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	mingo@...nel.org, brgerst@...il.com, torvalds@...ux-foundation.org,
	x86@...nel.org, linux-kernel@...r.kernel.org, hpa@...or.com,
	dvlasenk@...hat.com, bp@...e.de, tglx@...utronix.de,
	jpoimboe@...hat.com
Subject: Re: [PATCH v3 0/7] x86: Rewrite switch_to()

Andy Lutomirski <luto@...capital.net> wrote:
>
> I will be quite surprised if you can measure any effect at all.  I've
> never seen context switches take fewer than ~2k cycles, and on my
> laptop, they take 8k-9k cycles.  The scheduler is really, really slow.

Indeed, I think I still have a bugzilla entry somewhere regarding
the huge performance regression when we first switched over to the
current scheduler.

Over the years people have been trying to hack around it, e.g.,
network driver polling, low latency socket, anything to avoid
going into the scheduler.  We really should fix it properly some
day.

Cheers,
-- 
Email: Herbert Xu <herbert@...dor.apana.org.au>
Home Page: http://gondor.apana.org.au/~herbert/
PGP Key: http://gondor.apana.org.au/~herbert/pubkey.txt