Re: [PATCH 1/1] add StartTimeMonotomic, StartTimeBootTime to per pid in /proc

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



On Wed, 22.01.14 16:53, Peter Zijlstra (peterz@xxxxxxxxxxxxx) wrote:

> 
> On Tue, Jan 21, 2014 at 07:10:04AM -0800, Dan Ballard wrote:
> > starttime in /proc/$PID/stat is inaccurate by "clock tick" granularity.
> > The kernel keeps better track os this exposes that in /prod/$PID/status
> > as StartTimeMonotonic and StartTimeBootTime
> 
> Why?

Well, the canonical way to expose clocks to userspace these days is with
CLOCK_MONOTONIC, CLOCK_BOOTTIME, and so on. The starttime is currently
exposed in a way that is made inaccurate by the clock tick in
/proc/$PID/stat. Dan's patch simply unfucks that interface.

The process starttime is useful for a variety of things, like figuring
out creation ordering of processes. Or it is useful to detect PID
reuses in a somewhat reliable way. It is useful information to show the
admin in "ps". Profilers like "bootchart" can use this information to
plot when precisely specific process got started. From the outside it is
often useful to see for how long a specific process has already been
running, for accounting needs, and so on.

Note that Dan's patch doesn't add any new timestamp logic to the kernel,
it just exposes the existing timestamps in a way to userspace that is
more in line with the rest of timestamps exposed. 

Lennart
--
To unsubscribe from this list: send the line "unsubscribe linux-doc" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Index of Archives]     [Kernel Newbies]     [Security]     [Netfilter]     [Bugtraq]     [Linux FS]     [Yosemite Forum]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux RAID]     [Samba]     [Video 4 Linux]     [Device Mapper]     [Linux Resources]

  Powered by Linux