linux-kernel - Re: Restartable Sequences system call merged into Linux

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Message-ID: <48a0d905-2568-51b8-80c9-a20ecaa25f9b@redhat.com>
Date:   Thu, 14 Jun 2018 16:00:32 +0200
From:   Florian Weimer <fweimer@...hat.com>
To:     Pavel Machek <pavel@....cz>,
        Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
Cc:     carlos <carlos@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Boqun Feng <boqun.feng@...il.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        libc-alpha <libc-alpha@...rceware.org>
Subject: Re: Restartable Sequences system call merged into Linux

On 06/14/2018 03:49 PM, Pavel Machek wrote:
> Hi!
> 
>>>> - rseq_preempt(): on preemption, the scheduler sets the TIF_NOTIFY_RESUME thread
>>>>    flag, so rseq_handle_notify_resume() can check whether it's in a rseq critical
>>>>    section when returning to user-space,
>>>> - rseq_signal_deliver(): on signal delivery, rseq_handle_notify_resume() checks
>>>>    whether it's in a rseq critical section,
>>>> - rseq_migrate: on migration, the scheduler sets TIF_NOTIFY_RESUME as well,
>>>
>>> Yes, this is not likely to be noticeable.
>>>
>>> But the proposal wanted to add a syscall to thread creation, right?
>>> And I believe that may be noticeable.
>>
>> Fair point! Do we have a standard benchmark that would stress this ?
> 
> Web server performance benchmarks basically test clone() performance
> in many cases.

Isn't that fork?  I expect that the rseq arena is inherited on fork and 
fork-type clone, otherwise it's going to be painful.

Thanks,
Florian