linux-kernel - [PATCH RFC 0/5] x86,fpu: make FPU context switching much lazier

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Message-Id: <1475353895-22175-1-git-send-email-riel@redhat.com>
Date:   Sat,  1 Oct 2016 16:31:30 -0400
From:   riel@...hat.com
To:     linux-kernel@...r.kernel.org
Cc:     x86@...nel.org, tglx@...utronix.de, pbonzini@...hat.com,
        mingo@...hat.com, luto@...nel.org, hpa@...or.com,
        dave.hansen@...ux.intel.com, bp@...e.de
Subject: [PATCH RFC 0/5] x86,fpu: make FPU context switching much lazier

This series is an attempt at making the x86 FPU context switching
code much lazier.  By only reloading the FPU context when a task
switches to user mode, we can avoid switching FPU context for tasks
that spin in kernel mode, and avoid reloading the FPU context for
tasks that get interrupted by a kernel thread or briefly go idle.

It also allows us to skip restoring the userspace FPU context when
exiting a KVM guest.

This series is still BROKEN.  The first 3 patches seem to work
fine in my tests (but should not, due to missing signal path
code), while the 4th test makes it easier to trigger bugs.

I am posting this to ask about obvious issues people may see,
ideas on what direction I should take this series in, and to
avoid code conflicts with Andy's plans wrt. lazy fpu mode.