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From: Christian Borntraeger <borntraeger@de.ibm.com>
To: Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Marcelo Tosatti <mtosatti@redhat.com>,
	Ingo Molnar <mingo@redhat.com>, Avi Kivity <avi@redhat.com>,
	Rik van Riel <riel@redhat.com>, S390 <linux-s390@vger.kernel.org>,
	Carsten Otte <cotte@de.ibm.com>, KVM <kvm@vger.kernel.org>,
	chegu vinod <chegu_vinod@hp.com>,
	"Andrew M. Theurer" <habanero@linux.vnet.ibm.com>,
	LKML <linux-kernel@vger.kernel.org>, X86 <x86@kernel.org>,
	Gleb Natapov <gleb@redhat.com>,
	linux390@de.ibm.com,
	Srivatsa Vaddagiri <srivatsa.vaddagiri@gmail.com>,
	Joerg Roedel <joerg.roedel@amd.com>
Subject: Re: [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler
Date: Mon, 09 Jul 2012 09:55:10 +0200	[thread overview]
Message-ID: <4FFA8E5E.3070108@de.ibm.com> (raw)
In-Reply-To: <20120709062012.24030.37154.sendpatchset@codeblue>

On 09/07/12 08:20, Raghavendra K T wrote:
> Currently Pause Looop Exit (PLE) handler is doing directed yield to a
> random VCPU on PL exit. Though we already have filtering while choosing
> the candidate to yield_to, we can do better.
> 
> Problem is, for large vcpu guests, we have more probability of yielding
> to a bad vcpu. We are not able to prevent directed yield to same guy who
> has done PL exit recently, who perhaps spins again and wastes CPU.
> 
> Fix that by keeping track of who has done PL exit. So The Algorithm in series
> give chance to a VCPU which has:


We could do the same for s390. The appropriate exit would be diag44 (yield to hypervisor).

Almost all s390 kernels use diag9c (directed yield to a given guest cpu) for spinlocks, though.
So there is no win here, but there are other cases were diag44 is used, e.g. cpu_relax.
I have to double check with others, if these cases are critical, but for now, it seems 
that your dummy implementation  for s390 is just fine. After all it is a no-op until 
we implement something.

Thanks

Christian


  parent reply	other threads:[~2012-07-09  7:55 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-07-09  6:20 [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler Raghavendra K T
2012-07-09  6:20 ` [PATCH RFC 1/2] kvm vcpu: Note down pause loop exit Raghavendra K T
2012-07-09  6:33   ` Raghavendra K T
2012-07-09  6:33     ` Raghavendra K T
2012-07-09 22:39   ` Rik van Riel
2012-07-10 11:22     ` Raghavendra K T
2012-07-11  8:53   ` Avi Kivity
2012-07-11 10:52     ` Raghavendra K T
2012-07-11 11:18       ` Avi Kivity
2012-07-11 11:56         ` Raghavendra K T
2012-07-11 12:41           ` Andrew Jones
2012-07-12 10:58       ` Nikunj A Dadhania
2012-07-12 11:02         ` Raghavendra K T
2012-07-09  6:20 ` [PATCH RFC 2/2] kvm PLE handler: Choose better candidate for directed yield Raghavendra K T
2012-07-09 22:30   ` Rik van Riel
2012-07-10 11:46     ` Raghavendra K T
2012-07-09  7:55 ` Christian Borntraeger [this message]
2012-07-10  8:27   ` [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler Raghavendra K T
2012-07-11  9:06   ` Avi Kivity
2012-07-11 10:17     ` Christian Borntraeger
2012-07-11 11:04       ` Avi Kivity
2012-07-11 11:16         ` Alexander Graf
2012-07-11 11:23           ` Avi Kivity
2012-07-11 11:52             ` Alexander Graf
2012-07-11 12:48               ` Avi Kivity
2012-07-12  2:19             ` Benjamin Herrenschmidt
2012-07-11 11:18         ` Christian Borntraeger
2012-07-11 11:39           ` Avi Kivity
2012-07-12  5:11             ` Raghavendra K T
2012-07-12  8:11               ` Avi Kivity
2012-07-12  8:32                 ` Raghavendra K T
2012-07-12  2:17         ` Benjamin Herrenschmidt
2012-07-12  8:12           ` Avi Kivity
2012-07-12 11:24             ` Benjamin Herrenschmidt
2012-07-12 10:38         ` Nikunj A Dadhania
2012-07-11 11:51       ` Raghavendra K T
2012-07-11 11:55         ` Christian Borntraeger
2012-07-11 12:04           ` Raghavendra K T
2012-07-11 13:04         ` Raghavendra K T
2012-07-09 21:47 ` Andrew Theurer
2012-07-09 21:47   ` Andrew Theurer
2012-07-10  9:26   ` Raghavendra K T
2012-07-10 10:07   ` [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler : detailed result Raghavendra K T
2012-07-10 11:54   ` [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler Raghavendra K T
2012-07-10 13:27     ` Andrew Theurer
2012-07-11  9:00   ` Avi Kivity
2012-07-11 13:59     ` Raghavendra K T
2012-07-11 14:01       ` Raghavendra K T
2012-07-12  8:15         ` Avi Kivity
2012-07-12  8:25           ` Raghavendra K T
2012-07-12 12:31             ` Avi Kivity
2012-07-09 22:28 ` Rik van Riel

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