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Date: Thu, 16 Jun 2011 12:26:06 +0200
From: Ingo Molnar <mingo@elte.hu>
Message-ID: <20110616102606.GA24541@elte.hu>
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Subject: Re: [Qemu-devel] [RFC][PATCH] Register Linux dyntick timer as
	per-thread signal
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To: Jan Kiszka <jan.kiszka@siemens.com>
Cc: Anthony Liguori <aliguori@us.ibm.com>, kvm <kvm@vger.kernel.org>, Asias He <asias.hejun@gmail.com>, qemu-devel <qemu-devel@nongnu.org>, Pekka Enberg <penberg@cs.helsinki.fi>, Sasha Levin <levinsasha928@gmail.com>, Paolo Bonzini <pbonzini@redhat.com>


* Jan Kiszka <jan.kiszka@siemens.com> wrote:

> Ingo Molnar pointed out that sending the timer signal to the whole
> process, just blocking it everywhere, is suboptimal with an increasing
> number of threads. QEMU is using this pattern so far.
> 
> But Linux provides a (non-portable) way to restrict the signal to a
> single thread: Use SIGEV_THREAD_ID unless we are forced to emulate
> signalfd via an additional thread. That case could theoretically be
> optimized as well, but it doesn't look worth bothering.

Would be nice to mention it in the changelog that the context and 
motivation for my remark was a patch sent for tools/kvm/ by Asias He:

  kvm tools: Block SIGALRM for vcpu thread using sig_block() helper

Thanks,

	Ingo