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
