From: john stultz <johnstul@us.ibm.com>
To: Andrew Lutomirski <luto@mit.edu>
Cc: Arun Sharma <asharma@fb.com>,
linux-kernel@vger.kernel.org, Kumar Sundararajan <kumar@fb.com>,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@elte.hu>, Thomas Gleixner <tglx@linutronix.de>
Subject: Re: [PATCH 2/2] Add a thread cpu time implementation to vDSO
Date: Mon, 12 Dec 2011 15:52:53 -0800 [thread overview]
Message-ID: <1323733973.4078.116.camel@work-vm> (raw)
In-Reply-To: <CAObL_7H_2H3f=+UwJ_DEGAVYbQY_ekj+a+BQf6qyFrtU4mqnAw@mail.gmail.com>
On Mon, 2011-12-12 at 15:41 -0800, Andrew Lutomirski wrote:
> On Mon, Dec 12, 2011 at 3:32 PM, john stultz <johnstul@us.ibm.com> wrote:
> > Is it just that you're concerned about the clockid switch costs being
> > too high?
>
> From my (old, from memory) measurements, the switch cost is very very
> low if it's predicted correctly, and the main case where it's likely
> to be mispredicted is when it hasn't been called in awhile, in which
> case either probably no one cares or the cache misses will dominate.
>
> How worried are you about introducing a year 2554 bug? Python says:
>
> >>> dateutil.parser.parse('1/1/1970') + datetime.timedelta(seconds = 2**64 // 1000000000)
> datetime.datetime(2554, 7, 21, 23, 34, 33)
Not very. :)
Worse case the syscall can expose a nsec_t or something that can be
bumped to u128 when that becomes common.
thanks
-john
next prev parent reply other threads:[~2011-12-12 23:53 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2011-12-12 19:36 [PATCH 0/2] Add a thread cpu time implementation to vDSO Arun Sharma
2011-12-12 19:36 ` [PATCH 1/2] Extend VVAR support to multiple pages Arun Sharma
2011-12-12 19:36 ` [PATCH 2/2] Add a thread cpu time implementation to vDSO Arun Sharma
2011-12-12 20:13 ` Eric Dumazet
2011-12-12 21:19 ` Arun Sharma
2011-12-12 21:27 ` Eric Dumazet
2011-12-12 21:33 ` Andrew Lutomirski
2011-12-12 22:14 ` Arun Sharma
2011-12-13 8:52 ` Peter Zijlstra
2011-12-13 18:15 ` Arun Sharma
2011-12-13 18:53 ` Peter Zijlstra
2011-12-12 20:15 ` Andrew Lutomirski
2011-12-12 22:49 ` Arun Sharma
2011-12-12 23:01 ` Andrew Lutomirski
2011-12-13 0:40 ` Arun Sharma
2011-12-12 23:09 ` john stultz
2011-12-12 23:20 ` Arun Sharma
2011-12-12 23:32 ` john stultz
2011-12-12 23:41 ` Andrew Lutomirski
2011-12-12 23:52 ` john stultz [this message]
2011-12-13 0:26 ` Arun Sharma
-- strict thread matches above, loose matches on Subject: below --
2011-12-19 19:51 [PATCH 0/2] Add a thread cpu time implementation to vDSO (v2) Arun Sharma
2011-12-19 19:51 ` [PATCH 2/2] Add a thread cpu time implementation to vDSO Arun Sharma
2011-12-19 19:58 ` Arun Sharma
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