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From: Paolo Bonzini <pbonzini@redhat.com>
To: Christian Borntraeger <borntraeger@de.ibm.com>,
	Christoffer Dall <christoffer.dall@linaro.org>,
	kvmarm@lists.cs.columbia.edu, kvm@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org
Cc: Marc Zyngier <marc.zyngier@arm.com>
Subject: Re: [PATCH v2] arm/arm64: KVM: Properly account for guest CPU time
Date: Mon, 01 Jun 2015 13:34:53 +0200	[thread overview]
Message-ID: <556C435D.3050900@redhat.com> (raw)
In-Reply-To: <556C0E22.9090401@de.ibm.com>



On 01/06/2015 09:47, Christian Borntraeger wrote:
> 
> 1: "disable", "guest", "disable again and save", "restore to disable", "enable"
> and now it is
> 2: "disable", "guest", "enable"
> and with your patch it is
> 3: "disable", "guest", "enable", "disable, "enable"
> 
> I assume that 3 and 1 are similar in its costs, so this is probably ok.

At least on x86, 3 and 2 are similar, but 3 is much more expensive than
1!  See https://lkml.org/lkml/2015/5/5/835:

Cost of: CLI                         insn  same-IF :     0 cycles
Cost of: CLI                         insn  flip-IF :     0 cycles
Cost of: STI                         insn  same-IF :     0 cycles
Cost of: STI                         insn  flip-IF :     0 cycles
Cost of: PUSHF                       insn          :     0 cycles
Cost of: POPF                        insn  same-IF :    20 cycles
Cost of: POPF                        insn  flip-IF :    28 cycles
Cost of: local_irq_save()            fn            :    20 cycles
Cost of: local_irq_restore()         fn    same-IF :    24 cycles
Cost of: local_irq_restore()         fn    flip-IF :    28 cycles
Cost of: irq_save()+restore()        fn    same-IF :    48 cycles
Cost of: irq_save()+restore()        fn    flip-IF :    48 cycles

Paolo

WARNING: multiple messages have this Message-ID (diff)
From: pbonzini@redhat.com (Paolo Bonzini)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH v2] arm/arm64: KVM: Properly account for guest CPU time
Date: Mon, 01 Jun 2015 13:34:53 +0200	[thread overview]
Message-ID: <556C435D.3050900@redhat.com> (raw)
In-Reply-To: <556C0E22.9090401@de.ibm.com>



On 01/06/2015 09:47, Christian Borntraeger wrote:
> 
> 1: "disable", "guest", "disable again and save", "restore to disable", "enable"
> and now it is
> 2: "disable", "guest", "enable"
> and with your patch it is
> 3: "disable", "guest", "enable", "disable, "enable"
> 
> I assume that 3 and 1 are similar in its costs, so this is probably ok.

At least on x86, 3 and 2 are similar, but 3 is much more expensive than
1!  See https://lkml.org/lkml/2015/5/5/835:

Cost of: CLI                         insn  same-IF :     0 cycles
Cost of: CLI                         insn  flip-IF :     0 cycles
Cost of: STI                         insn  same-IF :     0 cycles
Cost of: STI                         insn  flip-IF :     0 cycles
Cost of: PUSHF                       insn          :     0 cycles
Cost of: POPF                        insn  same-IF :    20 cycles
Cost of: POPF                        insn  flip-IF :    28 cycles
Cost of: local_irq_save()            fn            :    20 cycles
Cost of: local_irq_restore()         fn    same-IF :    24 cycles
Cost of: local_irq_restore()         fn    flip-IF :    28 cycles
Cost of: irq_save()+restore()        fn    same-IF :    48 cycles
Cost of: irq_save()+restore()        fn    flip-IF :    48 cycles

Paolo

  parent reply	other threads:[~2015-06-01 11:34 UTC|newest]

Thread overview: 42+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-05-28 18:49 [PATCH v2] arm/arm64: KVM: Properly account for guest CPU time Christoffer Dall
2015-05-28 18:49 ` Christoffer Dall
2015-05-29 22:34 ` Mario Smarduch
2015-05-29 22:34   ` Mario Smarduch
2015-05-31  6:59   ` Christoffer Dall
2015-05-31  6:59     ` Christoffer Dall
2015-06-01 15:48     ` Mario Smarduch
2015-06-01 15:48       ` Mario Smarduch
2015-06-02  9:27       ` Christoffer Dall
2015-06-02  9:27         ` Christoffer Dall
2015-06-02 11:55         ` Christoffer Dall
2015-06-02 11:55           ` Christoffer Dall
2015-06-05 12:24         ` Mario Smarduch
2015-06-05 12:24           ` Mario Smarduch
2015-06-08 11:35           ` Christoffer Dall
2015-06-08 11:35             ` Christoffer Dall
2015-06-09 23:04             ` Mario Smarduch
2015-06-09 23:04               ` Mario Smarduch
2015-06-01  7:47 ` Christian Borntraeger
2015-06-01  7:47   ` Christian Borntraeger
2015-06-01  9:08   ` Christoffer Dall
2015-06-01  9:08     ` Christoffer Dall
2015-06-01  9:21     ` Christian Borntraeger
2015-06-01  9:21       ` Christian Borntraeger
2015-06-01 13:35       ` Christoffer Dall
2015-06-01 13:35         ` Christoffer Dall
2015-06-01 13:37         ` Christian Borntraeger
2015-06-01 13:37           ` Christian Borntraeger
2015-06-02  9:28           ` Christoffer Dall
2015-06-02  9:28             ` Christoffer Dall
2015-06-01 11:34   ` Paolo Bonzini [this message]
2015-06-01 11:34     ` Paolo Bonzini
2015-06-01 11:42     ` Christian Borntraeger
2015-06-01 11:42       ` Christian Borntraeger
2015-06-01 11:52       ` Paolo Bonzini
2015-06-01 11:52         ` Paolo Bonzini
2015-06-08 17:50 ` Marc Zyngier
2015-06-08 17:50   ` Marc Zyngier
2015-06-09 14:43   ` Christoffer Dall
2015-06-09 14:43     ` Christoffer Dall
2015-06-09 16:39     ` Marc Zyngier
2015-06-09 16:39       ` Marc Zyngier

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