linux-kernel - Re: [Xen-devel] [RFC v4 2/2] x86/xen: allow privcmd hypercalls to be preempted

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Date:	Mon, 26 Jan 2015 10:46:03 +0000
From:	"Jan Beulich" <JBeulich@...e.com>
To:	"Luis R. Rodriguez" <mcgrof@...e.com>
Cc:	"Andy Lutomirski" <luto@...capital.net>,
	"David Vrabel" <david.vrabel@...rix.com>,
	"Luis R. Rodriguez" <mcgrof@...not-panic.com>,
	<rostedt@...dmis.org>,
	"Masami Hiramatsu" <masami.hiramatsu.pt@...achi.com>,
	<x86@...nel.org>, "Thomas Gleixner" <tglx@...utronix.de>,
	<paulmck@...ux.vnet.ibm.com>, <xen-devel@...ts.xenproject.org>,
	<boris.ostrovsky@...cle.com>, <konrad.wilk@...cle.com>,
	"Ingo Molnar" <mingo@...hat.com>, "Borislav Petkov" <bp@...e.de>,
	<kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [Xen-devel] [RFC v4 2/2] x86/xen: allow privcmd hypercalls
 to be preempted

>>> On 23.01.15 at 19:58, <mcgrof@...e.com> wrote:
> On Fri, Jan 23, 2015 at 11:45:06AM +0000, David Vrabel wrote:
>> On 23/01/15 00:29, Luis R. Rodriguez wrote:
>> > @@ -1243,6 +1247,25 @@ void xen_evtchn_do_upcall(struct pt_regs *regs)
>> >  	set_irq_regs(old_regs);
>> >  }
>> >  
>> > +/*
>> > + * CONFIG_PREEMPT=n kernels can end up triggering the softlock
>> > + * TASK_UNINTERRUPTIBLE hanger check (default 120 seconds)
>> > + * when certain multicalls are used [0] on large systems, in
>> > + * that case we need a way to voluntarily preempt. This is
>> > + * only an issue on CONFIG_PREEMPT=n kernels.
>> 
>> Rewrite this comment as;
>> 
>> * Some hypercalls issued by the toolstack can take many 10s of
> 
> Its not just hypercalls though, this is all about the interactions
> with multicalls no?

multicalls are just a special case of hypercalls.

Jan

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