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

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Message-ID: <20141211203921.GP25677@wotan.suse.de>
Date:	Thu, 11 Dec 2014 21:39:21 +0100
From:	"Luis R. Rodriguez" <mcgrof@...e.com>
To:	"H. Peter Anvin" <hpa@...or.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 Thu, Dec 11, 2014 at 10:47:44AM -0800, H. Peter Anvin wrote:
> 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.

If you mean architecture and design then yes however this patch tries
to look for a resolution with the existing architecture.

  Luis
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