From: Paolo Bonzini <pbonzini@redhat.com>
To: James Hogan <james.hogan@imgtec.com>
Cc: Andreas Herrmann <andreas.herrmann@caviumnetworks.com>,
Gleb Natapov <gleb@kernel.org>,
kvm@vger.kernel.org, Ralf Baechle <ralf@linux-mips.org>,
linux-mips@linux-mips.org, David Daney <david.daney@cavium.com>,
Sanjay Lal <sanjayl@kymasys.com>
Subject: Re: [PATCH v2 00/23] MIPS: KVM: Fixes and guest timer rewrite
Date: Fri, 30 May 2014 09:57:18 +0200 [thread overview]
Message-ID: <538839DE.3000804@redhat.com> (raw)
In-Reply-To: <53879C3E.3040102@imgtec.com>
Il 29/05/2014 22:44, James Hogan ha scritto:
> Yes, I agree with your analysis and had considered something like this,
> although it doesn't particularly appeal to my sense of perfectionism :).
I can see that. But I think the simplification of the code is worth it.
It is hard to explain why the invalid times-goes-backwards case can
happen if env->count_save_time is overwritten with data from another
machine. I think the explanation is that (due to
timers_state.cpu_ticks_enabled) the value of "cpu_get_clock_at(now) -
env->count_save_time" does not depend on get_clock(), but the code
doesn't have any comment for that.
Rather than adding comments, we might as well force it to be always zero
and just write get_clock() to COUNT_RESUME.
Finally, having to serialize env->count_save_time makes harder to
support migration from TCG to KVM and back.
> It would be race free though, and if you're stopping the VM at all you
> expect to lose some time anyway.
Since you mentioned perfectionism, :) your code also loses some time;
COUNT_RESUME is written based on when the CPU state becomes clean, not
on when the CPU was restarted.
Paolo
next prev parent reply other threads:[~2014-05-30 7:57 UTC|newest]
Thread overview: 40+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-05-29 9:16 [PATCH v2 00/23] MIPS: KVM: Fixes and guest timer rewrite James Hogan
2014-05-29 9:16 ` [PATCH v2 01/23] MIPS: KVM: Allocate at least 16KB for exception handlers James Hogan
2014-05-29 9:16 ` [PATCH v2 02/23] MIPS: Export local_flush_icache_range for KVM James Hogan
2014-05-30 10:18 ` Ralf Baechle
2014-05-29 9:16 ` [PATCH v2 03/23] MIPS: KVM: Use local_flush_icache_range to fix RI on XBurst James Hogan
2014-05-29 9:16 ` [PATCH v2 04/23] MIPS: KVM: Use tlb_write_random James Hogan
2014-05-29 9:16 ` [PATCH v2 05/23] MIPS: KVM: Add CP0_EPC KVM register access James Hogan
2014-05-29 9:16 ` [PATCH v2 06/23] MIPS: KVM: Move KVM_{GET,SET}_ONE_REG definitions into kvm_host.h James Hogan
2014-05-29 9:16 ` [PATCH v2 07/23] MIPS: KVM: Add CP0_Count/Compare KVM register access James Hogan
2014-05-29 9:16 ` [PATCH v2 08/23] MIPS: KVM: Add CP0_UserLocal " James Hogan
2014-05-29 9:16 ` [PATCH v2 09/23] MIPS: KVM: Add CP0_HWREna " James Hogan
2014-05-29 9:16 ` [PATCH v2 10/23] MIPS: KVM: Deliver guest interrupts after local_irq_disable() James Hogan
2014-05-29 9:16 ` [PATCH v2 11/23] MIPS: KVM: Fix timer race modifying guest CP0_Cause James Hogan
2014-05-29 10:36 ` Paolo Bonzini
2014-05-29 10:55 ` James Hogan
2014-05-29 11:31 ` Paolo Bonzini
2014-05-29 9:16 ` [PATCH v2 12/23] MIPS: KVM: Migrate hrtimer to follow VCPU James Hogan
2014-05-29 9:16 ` [PATCH v2 13/23] MIPS: KVM: Rewrite count/compare timer emulation James Hogan
2014-05-29 9:16 ` [PATCH v2 14/23] MIPS: KVM: Override guest kernel timer frequency directly James Hogan
2014-05-30 10:18 ` Ralf Baechle
2014-05-29 9:16 ` [PATCH v2 15/23] MIPS: KVM: Add master disable count interface James Hogan
2014-05-29 9:16 ` [PATCH v2 16/23] MIPS: KVM: Add count frequency KVM register James Hogan
2014-05-29 9:16 ` [PATCH v2 17/23] MIPS: KVM: Make kvm_mips_comparecount_{func,wakeup} static James Hogan
2014-05-29 9:16 ` [PATCH v2 18/23] MIPS: KVM: Whitespace fixes in kvm_mips_callbacks James Hogan
2014-05-29 9:16 ` [PATCH v2 19/23] MIPS: KVM: Fix kvm_debug bit-rottage James Hogan
2014-05-29 9:16 ` [PATCH v2 20/23] MIPS: KVM: Remove ifdef DEBUG around kvm_debug James Hogan
2014-05-29 9:16 ` [PATCH v2 21/23] MIPS: KVM: Quieten kvm_info() logging James Hogan
2014-05-29 9:16 ` [PATCH v2 22/23] MIPS: KVM: Remove redundant NULL checks before kfree() James Hogan
2014-05-29 9:16 ` [PATCH v2 23/23] MIPS: KVM: Remove redundant semicolon James Hogan
2014-05-29 10:36 ` [PATCH v2 00/23] MIPS: KVM: Fixes and guest timer rewrite Paolo Bonzini
2014-05-29 14:41 ` James Hogan
2014-05-29 15:23 ` Paolo Bonzini
2014-05-29 16:27 ` James Hogan
2014-05-29 17:03 ` Paolo Bonzini
2014-05-29 20:44 ` James Hogan
2014-05-30 7:57 ` Paolo Bonzini [this message]
2014-06-16 16:29 ` James Hogan
2014-06-16 16:33 ` Paolo Bonzini
2014-05-30 11:07 ` Paolo Bonzini
2014-05-30 16:16 ` James Hogan
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