From: Mathieu Desnoyers <mathieu.desnoyers@efficios•com>
To: Avi Kivity <avi@scylladb•com>
Cc: Nicholas Piggin <npiggin@gmail•com>,
"Paul E. McKenney" <paulmck@linux•vnet.ibm.com>,
linux-kernel <linux-kernel@vger•kernel.org>,
Ingo Molnar <mingo@kernel•org>,
Lai Jiangshan <jiangshanlai@gmail•com>,
dipankar <dipankar@in•ibm.com>,
Andrew Morton <akpm@linux-foundation•org>,
Josh Triplett <josh@joshtriplett•org>,
Thomas Gleixner <tglx@linutronix•de>,
Peter Zijlstra <peterz@infradead•org>,
rostedt <rostedt@goodmis•org>,
David Howells <dhowells@redhat•com>,
Eric Dumazet <edumazet@google•com>, fweisbec <fweisbec@gmail•com>,
Oleg Nesterov <oleg@redhat•com>,
Boqun Feng <boqun.feng@gmail•com>, Andrew Hunter <ahh@google•com>,
maged michael <maged.michael@gmail•com>,
gromer <gromer@google•com>,
Benjamin Herrenschmidt <benh@kernel•crashing.org>,
Paul Mackerras <paulus@samba•org>,
Michael Ellerman <mpe@ellerman•id.au>,
Dave Watson <davejwatson@fb•com>,
Alan Stern <stern@rowland•harvard.edu>,
Will Deacon <will.deacon@arm•com>,
Andy Lutomirski <luto@kernel•org>, Ingo Molnar <mingo@redhat•com>,
Alexander Viro <viro@zeniv•linux.org.uk>,
linuxppc-dev <linuxppc-dev@lists•ozlabs.org>,
linux-arch <linux-arch@vger•kernel.org>
Subject: Re: [PATCH tip/core/rcu 1/3] membarrier: Provide register expedited private command
Date: Thu, 5 Oct 2017 15:54:38 +0000 (UTC) [thread overview]
Message-ID: <1765353553.31703.1507218878562.JavaMail.zimbra@efficios.com> (raw)
In-Reply-To: <64c8984c-7140-ccce-513f-6b3f601257a7@scylladb.com>
----- On Oct 5, 2017, at 8:22 AM, Avi Kivity avi@scylladb•com wrote:
> On 10/05/2017 07:23 AM, Nicholas Piggin wrote:
>> On Wed, 4 Oct 2017 14:37:53 -0700
>> "Paul E. McKenney" <paulmck@linux•vnet.ibm.com> wrote:
>>
>>> From: Mathieu Desnoyers <mathieu.desnoyers@efficios•com>
>>>
>>> Provide a new command allowing processes to register their intent to use
>>> the private expedited command.
>>>
>>> This allows PowerPC to skip the full memory barrier in switch_mm(), and
>>> only issue the barrier when scheduling into a task belonging to a
>>> process that has registered to use expedited private.
>>>
>>> Processes are now required to register before using
>>> MEMBARRIER_CMD_PRIVATE_EXPEDITED, otherwise that command returns EPERM.
>>>
>>> Changes since v1:
>>> - Use test_ti_thread_flag(next, ...) instead of test_thread_flag() in
>>> powerpc membarrier_arch_sched_in(), given that we want to specifically
>>> check the next thread state.
>>> - Add missing ARCH_HAS_MEMBARRIER_HOOKS in Kconfig.
>>> - Use task_thread_info() to pass thread_info from task to
>>> *_ti_thread_flag().
>>>
>>> Changes since v2:
>>> - Move membarrier_arch_sched_in() call to finish_task_switch().
>>> - Check for NULL t->mm in membarrier_arch_fork().
>>> - Use membarrier_sched_in() in generic code, which invokes the
>>> arch-specific membarrier_arch_sched_in(). This fixes allnoconfig
>>> build on PowerPC.
>>> - Move asm/membarrier.h include under CONFIG_MEMBARRIER, fixing
>>> allnoconfig build on PowerPC.
>>> - Build and runtime tested on PowerPC.
>>>
>>> Changes since v3:
>>> - Simply rely on copy_mm() to copy the membarrier_private_expedited mm
>>> field on fork.
>>> - powerpc: test thread flag instead of reading
>>> membarrier_private_expedited in membarrier_arch_fork().
>>> - powerpc: skip memory barrier in membarrier_arch_sched_in() if coming
>>> from kernel thread, since mmdrop() implies a full barrier.
>>> - Set membarrier_private_expedited to 1 only after arch registration
>>> code, thus eliminating a race where concurrent commands could succeed
>>> when they should fail if issued concurrently with process
>>> registration.
>>> - Use READ_ONCE() for membarrier_private_expedited field access in
>>> membarrier_private_expedited. Matches WRITE_ONCE() performed in
>>> process registration.
>>>
>>> Changes since v4:
>>> - Move powerpc hook from sched_in() to switch_mm(), based on feedback
>>> from Nicholas Piggin.
>> For now, the powerpc approach is okay by me. I plan to test
>> others (e.g., taking runqueue locks) on larger systems, but that can
>> be sent as an incremental patch at a later time.
>>
>> The main thing I would like is for people to review the userspace API.
>>
>
> As a future satisfied user of the expedited private membarrier syscall,
> I am happy with the change.
Thanks Avi for your input on the userspace API.
Mathieu
--
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com
next prev parent reply other threads:[~2017-10-05 15:53 UTC|newest]
Thread overview: 17+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20171004213734.GA11463@linux.vnet.ibm.com>
2017-10-04 21:37 ` [PATCH tip/core/rcu 1/3] membarrier: Provide register expedited private command Paul E. McKenney
2017-10-05 4:23 ` Nicholas Piggin
2017-10-05 12:22 ` Avi Kivity
2017-10-05 15:54 ` Mathieu Desnoyers [this message]
2017-10-05 15:53 ` Mathieu Desnoyers
2017-10-05 12:12 ` Peter Zijlstra
2017-10-05 12:24 ` Peter Zijlstra
2017-10-05 16:05 ` Mathieu Desnoyers
2017-10-05 16:02 ` Mathieu Desnoyers
2017-10-05 16:21 ` Peter Zijlstra
2017-10-05 21:44 ` Mathieu Desnoyers
2017-10-05 22:02 ` Andrea Parri
2017-10-05 22:04 ` Andrea Parri
2017-10-05 22:19 ` Mathieu Desnoyers
2017-10-05 22:46 ` Steven Rostedt
2017-10-06 8:32 ` Peter Zijlstra
2017-10-07 15:10 ` Andrea Parri
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