From: Oleg Nesterov <oleg@redhat.com>
To: riel@redhat.com
Cc: linux-kernel@vger.kernel.org, mingo@redhat.com, hpa@zytor.com,
matt.fleming@intel.com, bp@suse.de, pbonzini@redhat.com,
tglx@linutronix.de, luto@amacapital.net
Subject: Re: [RFC PATCH 04/11] x86,fpu: defer FPU restore until return to userspace
Date: Tue, 13 Jan 2015 18:11:34 +0100 [thread overview]
Message-ID: <20150113171134.GA27519@redhat.com> (raw)
In-Reply-To: <1421012793-30106-5-git-send-email-riel@redhat.com>
On 01/11, riel@redhat.com wrote:
>
> Defer restoring the FPU state, if so desired, until the task returns to
> userspace.
And I have another concern.
Afaocs with this patch the idle threads will run with TIF_LOAD_FPU set but
without fpu.has_fpu.
This is fine by itself, but this (performance-wise) breaks kernel_fpu_begin()
if use_eager_fpu() == T. Please see the changelog in 5187b28ff08249ab8a162e8
and note that this patch cc's @stable.
Yes, yes, even if I am right we should blame kernel_fpu_begin() and other
eager_fpu oddities. I tried to start the cleanups/fixes in this area some
time ago, but they were ignored.
Oleg.
next prev parent reply other threads:[~2015-01-13 17:12 UTC|newest]
Thread overview: 76+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-01-11 21:46 [RFC PATCH 0/11 BROKEN] move FPU context loading to userspace switch riel
2015-01-11 21:46 ` [RFC PATCH 01/11] x86,fpu: document the data structures a little riel
2015-01-12 21:18 ` Borislav Petkov
2015-01-12 21:38 ` Rik van Riel
2015-01-12 21:52 ` Dave Hansen
2015-01-13 15:59 ` Rik van Riel
2015-01-11 21:46 ` [RFC PATCH 02/11] x86,fpu: replace fpu_switch_t with a thread flag riel
2015-01-13 15:24 ` Oleg Nesterov
2015-01-13 16:35 ` Rik van Riel
2015-01-13 16:55 ` Oleg Nesterov
2015-01-11 21:46 ` [RFC PATCH 03/11] x86,fpu: move __thread_fpu_begin to when the task has the fpu riel
2015-01-13 15:24 ` Oleg Nesterov
2015-01-13 16:37 ` Rik van Riel
2015-01-11 21:46 ` [RFC PATCH 04/11] x86,fpu: defer FPU restore until return to userspace riel
2015-01-13 15:53 ` Oleg Nesterov
2015-01-13 17:07 ` Andy Lutomirski
2015-01-13 17:11 ` Oleg Nesterov [this message]
2015-01-13 17:18 ` Andy Lutomirski
2015-01-13 17:44 ` Rik van Riel
2015-01-13 17:57 ` Andy Lutomirski
2015-01-13 18:13 ` Rik van Riel
2015-01-13 18:26 ` Andy Lutomirski
2015-01-13 17:54 ` Rik van Riel
2015-01-13 18:22 ` Oleg Nesterov
2015-01-13 18:30 ` Oleg Nesterov
2015-01-13 20:06 ` Rik van Riel
2015-01-14 17:56 ` Oleg Nesterov
2015-01-13 17:58 ` Oleg Nesterov
2015-01-13 19:32 ` Rik van Riel
2015-01-11 21:46 ` [RFC PATCH 05/11] x86,fpu: ensure FPU state is reloaded from memory if task is traced riel
2015-01-13 16:19 ` Oleg Nesterov
2015-01-13 16:33 ` Rik van Riel
2015-01-13 16:50 ` Oleg Nesterov
2015-01-13 16:57 ` Rik van Riel
2015-01-11 21:46 ` [RFC PATCH 06/11] x86,fpu: lazily skip fpu restore with eager fpu mode, too riel
2015-01-13 17:11 ` Andy Lutomirski
2015-01-13 20:43 ` Rik van Riel
2015-01-14 18:36 ` Oleg Nesterov
2015-01-15 2:49 ` Rik van Riel
2015-01-15 19:34 ` Oleg Nesterov
2015-01-11 21:46 ` [RFC PATCH 07/11] x86,fpu: store current fpu pointer, instead of fpu_owner_task riel
2015-01-11 21:46 ` [RFC PATCH 08/11] x86,fpu: restore user FPU state lazily after __kernel_fpu_end riel
2015-01-14 18:43 ` Oleg Nesterov
2015-01-14 19:08 ` Oleg Nesterov
2015-01-11 21:46 ` [RFC PATCH 09/11] x86,fpu,kvm: keep vcpu FPU active as long as it is resident riel
2015-01-11 21:46 ` [RFC PATCH 10/11] x86,fpu: fix fpu_copy to deal with not-loaded fpu riel
2015-01-11 21:46 ` [RFC PATCH 11/11] (BROKEN) x86,fpu: broken signal handler stack setup riel
2015-01-15 19:19 ` [PATCH 0/3] x86, fpu: kernel_fpu_begin/end initial cleanups/fix Oleg Nesterov
2015-01-15 19:19 ` [PATCH 1/3] x86, fpu: introduce per-cpu "bool in_kernel_fpu" Oleg Nesterov
2015-01-16 2:22 ` Rik van Riel
2015-01-20 12:54 ` [tip:x86/fpu] x86, fpu: Introduce per-cpu in_kernel_fpu state tip-bot for Oleg Nesterov
2015-01-15 19:20 ` [PATCH 2/3] x86, fpu: don't abuse ->has_fpu in __kernel_fpu_{begin,end}() Oleg Nesterov
2015-01-16 2:27 ` Rik van Riel
2015-01-16 15:54 ` Oleg Nesterov
2015-01-16 16:07 ` Rik van Riel
2015-01-20 12:55 ` [tip:x86/fpu] x86, fpu: Don't abuse has_fpu in __kernel_fpu_begin /end() tip-bot for Oleg Nesterov
2015-01-15 19:20 ` [PATCH 3/3] x86, fpu: fix math_state_restore() race with kernel_fpu_begin() Oleg Nesterov
2015-01-16 2:30 ` Rik van Riel
2015-01-16 16:03 ` Oleg Nesterov
2015-01-20 12:55 ` [tip:x86/fpu] x86, fpu: Fix " tip-bot for Oleg Nesterov
2015-01-19 18:51 ` [PATCH 0/3] x86, fpu: more eagerfpu cleanups Oleg Nesterov
2015-01-19 18:51 ` [PATCH 1/3] x86, fpu: __kernel_fpu_begin() should clear fpu_owner_task even if use_eager_fpu() Oleg Nesterov
2015-01-20 14:15 ` Rik van Riel
2015-02-20 18:13 ` Borislav Petkov
2015-03-03 11:27 ` [tip:x86/fpu] x86/fpu: " tip-bot for Oleg Nesterov
2015-01-19 18:51 ` [PATCH 2/3] x86, fpu: always allow FPU in interrupt " Oleg Nesterov
2015-01-20 14:46 ` Rik van Riel
2015-01-20 22:46 ` Andy Lutomirski
2015-02-20 21:48 ` Borislav Petkov
2015-03-03 11:28 ` [tip:x86/fpu] x86/fpu: Always " tip-bot for Oleg Nesterov
2015-01-19 18:52 ` [PATCH 3/3] x86, fpu: don't abuse FPU in kernel threads " Oleg Nesterov
2015-01-20 14:53 ` Rik van Riel
2015-02-23 15:31 ` Borislav Petkov
2015-03-03 11:28 ` [tip:x86/fpu] x86/fpu: Don' t " tip-bot for Oleg Nesterov
2015-02-20 12:10 ` [PATCH 0/3] x86, fpu: more eagerfpu cleanups Borislav Petkov
2015-02-20 13:30 ` Oleg Nesterov
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