linux-kernel - Re: [PATCH v2 2/2] x86/xen: allow privcmd hypercalls to be preempted

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Message-ID: <5489E6D0.8020002@zytor.com>
Date:	Thu, 11 Dec 2014 10:47:44 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	"Luis R. Rodriguez" <mcgrof@...e.com>
CC:	"Luis R. Rodriguez" <mcgrof@...not-panic.com>, mingo@...hat.com,
	peterz@...radead.org, tglx@...utronix.de, konrad.wilk@...cle.com,
	david.vrabel@...rix.com, masami.hiramatsu.pt@...achi.com,
	rostedt@...dmis.org, luto@...capital.net, JBeulich@...e.com,
	jgross@...e.com, bpoirier@...e.de, x86@...nel.org,
	xen-devel@...ts.xenproject.org, linux-kernel@...r.kernel.org,
	Borislav Petkov <bp@...e.de>
Subject: Re: [PATCH v2 2/2] x86/xen: allow privcmd hypercalls to be preempted

On 12/10/2014 05:03 PM, Luis R. Rodriguez wrote:
> 
> This is an issue onloy for for non*-preemptive kernels.
> 
> Some of Xen's hypercalls can take a long time and unfortunately for
> *non*-preemptive kernels this can be quite a bit of an issue.
> We've handled situations like this with cond_resched() before which will
> push even *non*-preemptive kernels to behave as voluntarily preemptive,
> I was not aware to what extent this was done and precedents set but
> its pretety widespread now... this then just addresses once particular
> case where this is also an issuefor but now in IRQ context.
> 
> I agree its a hack but so are all the other cond_reshed() calls then.
> I don't think its a good idea to be spreading use of something like
> this everywhere but after careful review and trying toa void this
> exact code for a while I have not been able to find any other reasonable
> alternative.
> 

This sounds like a patch that is completely unrelated to the rest of the
patch.

	-hpa


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