[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [address@hidden: [PATCH] Make __getclktck return 100 for the Hurd]
From: |
Samuel Thibault |
Subject: |
Re: [address@hidden: [PATCH] Make __getclktck return 100 for the Hurd] |
Date: |
Tue, 18 Jun 2013 00:58:12 +0200 |
User-agent: |
Mutt/1.5.21+34 (58baf7c9f32f) (2010-12-30) |
Hello,
Roland McGrath, le Tue 11 Jun 2013 16:13:53 -0700, a écrit :
> > Basically, top doesn't report correct CPU times. This is caused by
> > sysconf() returning 1000000 while values read from /proc are true tick
> > counts, hence 100 per second at most.
>
> In fact, that is not a "true tick count". Most modern Linux kernels have
> ticks at 1024Hz, for example. The ABI for certain /proc/PID/* files is
> that certain fields are in centiseconds. That has nothing (except for an
> historical relationship) to do with the actual frequency used in the kernel.
Well, more or less so. It's centiseconds on x86, but other bases are
used on other archs.
> This is a bug in procfs, regardless. If it's a good idea to change what
> libc uses, then we'll change.
The problem is that applications such as top do assume that /proc is
expressed in _SC_CLK_TCK, which does indeed work on Linux: depending
on the arch, _SC_CLK_TCK will return the proper base for /proc. Other
applications simply hardcode /proc as being centiseconds-based. So
setting _SC_CLK_TCK to 100 and using centiseconds in /proc saves porting
headache in both cases.
Samuel