From: Rik van Riel <riel@redhat.com>
To: Ingo Molnar <mingo@kernel.org>, linux-kernel@vger.kernel.org
Cc: Andrew Morton <akpm@linux-foundation.org>,
Andy Lutomirski <luto@amacapital.net>,
Borislav Petkov <bp@alien8.de>,
Dave Hansen <dave.hansen@linux.intel.com>,
Fenghua Yu <fenghua.yu@intel.com>,
"H . Peter Anvin" <hpa@zytor.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Oleg Nesterov <oleg@redhat.com>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Yu-cheng Yu <yu-cheng.yu@intel.com>
Subject: Re: [PATCH 5/7] x86/fpu: Change fpu->fpregs_active users to fpu->fpstate_active
Date: Thu, 26 Jan 2017 09:44:12 -0500 [thread overview]
Message-ID: <1485441852.15964.49.camel@redhat.com> (raw)
In-Reply-To: <1485429989-23340-6-git-send-email-mingo@kernel.org>
On Thu, 2017-01-26 at 12:26 +0100, Ingo Molnar wrote:
> We want to simplify the FPU state machine by eliminating fpu-
> >fpregs_active,
> and we can do that because the two state flags (::fpregs_active and
> ::fpstate_active) are set essentially together.
>
> The old lazy FPU switching code used to make a distinction - but
> there's
> no lazy switching code anymore, we always switch in an 'eager'
> fashion.
I've been working for a while now to fix that for
KVM VCPU threads.
Currently when we switch to a VCPU thread, we first
load that thread's userspace FPU context, and then
soon after we save that, and load the guest side FPU
context.
When a VCPU thread goes idle, we also go through
two FPU context transitions.
In order to skip the unnecessary FPU context switches
for VCPU threads, I have been relying on separate
fpstate_active and fpregs_active states.
Do you have any ideas on how I could implement that
kind of change without separate fpstate_active and
fpregs_active states?
next prev parent reply other threads:[~2017-01-26 14:44 UTC|newest]
Thread overview: 22+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-26 11:26 [PATCH 0/7] x86/fpu: Simplify the FPU state machine Ingo Molnar
2017-01-26 11:26 ` [PATCH 1/7] x86/fpu: Simplify the fpu->last_cpu logic and rename it to fpu->fpregs_cached Ingo Molnar
2017-01-26 14:23 ` Rik van Riel
2017-01-26 14:53 ` Ingo Molnar
2017-01-26 15:05 ` [PATCH] x86/fpu: Unify the naming of the FPU register cache validity flags Ingo Molnar
2017-01-26 15:31 ` Peter Zijlstra
2017-01-26 14:54 ` [PATCH 1/7] x86/fpu: Simplify the fpu->last_cpu logic and rename it to fpu->fpregs_cached Rik van Riel
2017-01-26 15:09 ` Ingo Molnar
2017-01-26 16:51 ` Andy Lutomirski
2017-01-26 11:26 ` [PATCH 2/7] x86/fpu: Simplify fpu->fpregs_active use Ingo Molnar
2017-01-26 16:30 ` Andy Lutomirski
2017-01-26 11:26 ` [PATCH 3/7] x86/fpu: Make the fpu state change in fpu__clear() scheduler-atomic Ingo Molnar
2017-01-26 11:26 ` [PATCH 4/7] x86/fpu: Split the state handling in fpu__drop() Ingo Molnar
2017-01-26 11:26 ` [PATCH 5/7] x86/fpu: Change fpu->fpregs_active users to fpu->fpstate_active Ingo Molnar
2017-01-26 14:44 ` Rik van Riel [this message]
2017-01-26 15:16 ` Ingo Molnar
2017-01-26 15:45 ` Rik van Riel
2017-01-26 15:53 ` Ingo Molnar
2017-01-26 17:00 ` Andy Lutomirski
2017-01-26 18:04 ` Rik van Riel
2017-01-26 11:26 ` [PATCH 6/7] x86/fpu: Decouple fpregs_activate()/fpregs_deactivate() from fpu->fpregs_active Ingo Molnar
2017-01-26 11:26 ` [PATCH 7/7] x86/fpu: Remove struct fpu::fpregs_active Ingo Molnar
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