From: Andi Kleen <ak@linux.intel.com>
To: Arnd Bergmann <arnd@arndb.de>
Cc: Jens Axboe <axboe@kernel.dk>, Jan Kara <jack@suse.cz>,
Jeff Layton <jlayton@redhat.com>,
"Darrick J. Wong" <darrick.wong@oracle.com>,
y2038 Mailman List <y2038@lists.linaro.org>,
Brian Foster <bfoster@redhat.com>,
Miklos Szeredi <miklos@szeredi.hu>,
Pavel Tatashin <pasha.tatashin@oracle.com>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Linux FS-devel Mailing List <linux-fsdevel@vger.kernel.org>,
Alexander Viro <viro@zeniv.linux.org.uk>,
Andi Kleen <andi.kleen@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Deepa Dinamani <deepa.kernel@gmail.com>
Subject: Re: [PATCH] vfs: replace current_kernel_time64 with ktime equivalent
Date: Wed, 20 Jun 2018 09:19:18 -0700 [thread overview]
Message-ID: <87muvpsa61.fsf@linux.intel.com> (raw)
In-Reply-To: <CAK8P3a1J9j7pz-d+otbJweWgOZZePdaMJEb_sU2GJKi3oYq7Xg@mail.gmail.com> (Arnd Bergmann's message of "Wed, 20 Jun 2018 18:14:50 +0200")
Arnd Bergmann <arnd@arndb.de> writes:
>
> To clarify: current_kernel_time() uses at most millisecond resolution rather
> than microsecond, as tkr_mono.xtime_nsec only gets updated during the
> timer tick.
Ah you're right. I remember now: the motivation was to make sure there
is basically no overhead. In some setups the full gtod can be rather
slow, particularly if it falls back to some crappy timer.
I think it would be ok if it falls back to jiffies if TSC or a similar
fast timer doesn't work. But the function you're using likely
doesn't do that?
> Has that time scale changed over the past 16 years as CPUs got faster
> (and system call entry times slower down again with recent changes)?
Maybe a bit, but not substantially.
-Andi
next prev parent reply other threads:[~2018-06-20 16:19 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-06-20 15:01 [PATCH] vfs: replace current_kernel_time64 with ktime equivalent Arnd Bergmann
2018-06-20 15:40 ` Andi Kleen
2018-06-20 16:14 ` Arnd Bergmann
2018-06-20 16:19 ` Andi Kleen [this message]
2018-06-20 19:35 ` Arnd Bergmann
2018-06-25 13:42 ` Arnd Bergmann
2018-06-21 20:23 ` Dave Chinner
2018-06-22 13:24 ` Arnd Bergmann
2018-06-26 0:24 ` Dave Chinner
2018-06-26 16:08 ` [Y2038] " Arnd Bergmann
-- strict thread matches above, loose matches on Subject: below --
2018-07-26 13:07 Arnd Bergmann
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