From: Vallish Vaidyeshwara <vallish@amazon•com>
To: Richard Cochran <richardcochran@gmail•com>
Cc: <davem@davemloft•net>, <shuah@kernel•org>,
<netdev@vger•kernel.org>, <linux-kernel@vger•kernel.org>,
<eduval@amazon•com>, <anchalag@amazon•com>, <tglx@linutronix•de>
Subject: Re: [PATCH RESEND 0/2] enable hires timer to timeout datagram socket
Date: Tue, 22 Aug 2017 11:17:23 +0000 [thread overview]
Message-ID: <20170822111723.GB102755@amazon.com> (raw)
In-Reply-To: <20170822062311.okn7coroki2fjgyc@localhost>
On Tue, Aug 22, 2017 at 08:23:11AM +0200, Richard Cochran wrote:
> On Mon, Aug 21, 2017 at 06:22:10PM +0000, Vallish Vaidyeshwara wrote:
> > AWS Lambda is affected by this change in behavior in
> > system call. Following links has more information:
> > https://en.wikipedia.org/wiki/AWS_Lambda
>
> Quote:
>
> Unlike Amazon EC2, which is priced by the hour, AWS Lambda is
> metered in increments of 100 milliseconds.
>
> So I guess you want the accurate timeout in order to support billing?
> In any case, even with the old wheel you didn't have guarantees WRT
> timeout latency, and so the proper way for the application to handle
> this is to use a timerfd together with HIGH_RES_TIMERS, and PREEMPT_RT
> in order to have sub-millisecond latency.
>
> Thanks,
> Richard
Hello Richard,
4.4 kernel implementation of datagram socket wait code is calling
schedule_timeout() which in-turn calls __mod_timer(). __mod_timer()
does not add any slack. mod_timer() is the function that adds slack.
This gives good consistent results for event handling response time
on datagram socket timeouts.
strace from 4.4 test run of waiting for 180 seconds:
10:25:48.239685 setsockopt(3, SOL_SOCKET, SO_RCVTIMEO, "\264\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 16) = 0
10:25:48.239755 recvmsg(3, 0x7ffd0a3beec0, 0) = -1 EAGAIN (Resource temporarily unavailable)
10:28:48.236989 fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0
strace from 4.9 test run of waiting for 180 seconds times out close to 195 seconds:
setsockopt(3, SOL_SOCKET, SO_RCVTIMEO, "\264\0\0\0\0\0\0\0\0\0\0\0\0\0\0\0", 16) = 0 <0.000028>
recvmsg(3, 0x7ffd6a2c4380, 0) = -1 EAGAIN (Resource temporarily unavailable) <194.852000>
fstat(1, {st_mode=S_IFCHR|0620, st_rdev=makedev(136, 0), ...}) = 0 <0.000018>
This change of behavior in system call is breaking the application logic and
response time.
Thanks.
-Vallish
prev parent reply other threads:[~2017-08-22 11:17 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-08-18 18:44 [PATCH RESEND 0/2] enable hires timer to timeout datagram socket Vallish Vaidyeshwara
2017-08-18 18:44 ` [PATCH RESEND 1/2] net: enable high resolution timer mode to timeout datagram sockets Vallish Vaidyeshwara
2017-08-21 20:10 ` Cong Wang
2017-08-22 11:14 ` Vallish Vaidyeshwara
2017-08-18 18:44 ` [PATCH RESEND 2/2] selftests/net: add test to verify datagram socket timeout Vallish Vaidyeshwara
2017-08-18 20:18 ` [PATCH RESEND 0/2] enable hires timer to timeout datagram socket Richard Cochran
2017-08-18 22:27 ` Vallish Vaidyeshwara
2017-08-19 6:21 ` Richard Cochran
2017-08-20 1:47 ` Vallish Vaidyeshwara
2017-08-21 18:22 ` Vallish Vaidyeshwara
2017-08-22 6:23 ` Richard Cochran
2017-08-22 11:17 ` Vallish Vaidyeshwara [this message]
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