From: Christian Borntraeger <borntraeger@de.ibm.com> To: Paolo Bonzini <pbonzini@redhat.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 13:42:08 +0200 [thread overview] Message-ID: <556C4510.80704@de.ibm.com> (raw) In-Reply-To: <556C435D.3050900@redhat.com> Am 01.06.2015 um 13:34 schrieb Paolo Bonzini: > > > 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: That does not make sense. If 3 and 2 are similar, then 2 must be much more expensive than 1 as well. As 2 is a strict subset of 1 it must be cheaper, no? > > 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 Yes its similar on s390. local_irq_save/restore is noticable in guest exit hot loops (thats what inspired my patch), but a simple irq disable is just single cycle pipelined. Given the design of aggressive out-out order designs with all the architectural ordering this makes sense. Christian
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From: borntraeger@de.ibm.com (Christian Borntraeger) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH v2] arm/arm64: KVM: Properly account for guest CPU time Date: Mon, 01 Jun 2015 13:42:08 +0200 [thread overview] Message-ID: <556C4510.80704@de.ibm.com> (raw) In-Reply-To: <556C435D.3050900@redhat.com> Am 01.06.2015 um 13:34 schrieb Paolo Bonzini: > > > 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: That does not make sense. If 3 and 2 are similar, then 2 must be much more expensive than 1 as well. As 2 is a strict subset of 1 it must be cheaper, no? > > 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 Yes its similar on s390. local_irq_save/restore is noticable in guest exit hot loops (thats what inspired my patch), but a simple irq disable is just single cycle pipelined. Given the design of aggressive out-out order designs with all the architectural ordering this makes sense. Christian
next prev parent reply other threads:[~2015-06-01 11:42 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 2015-06-01 11:34 ` Paolo Bonzini 2015-06-01 11:42 ` Christian Borntraeger [this message] 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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