Messages in this thread | | | Subject | Re: Serious Kernel slowdown with HIMEM (4Gig) in 2.6.7 | Date | Sat, 14 Aug 2004 11:09:18 -0400 | From | "Lawrence E. Freil" <> |
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Darren, I ran your test of "ls -laR of /etc >/dev/null" on our system and you need to gen a kernel without himem and try it. I get around .1 seconds without himem and a whopping 4.45 with himem enabled.
I also tried without preemption and got the same results. It is strictly do to setting HIMEM in the kernel.
> Hi Lawrence > > On Fri, 13 Aug 2004, Lawrence E. Freil wrote: > > > Hello, > > > > I'm following the kernel bug reporting format so: > > > > 1. Linux 2.6.7 kernel slowdown in directory access with HIMEM on > > > > 2. I have discovered an issue with the Linux 2.6.7 kernel when HIMEM is > > enabled which exhibits itself as a slowdown in directory access regardless > > of filesystem used. When HIMEM is disabled the performance returns to > > normal. The test I ran was a simple "/usr/bin/time ls -l" of a directory > > with 3000 empty files. With HIMEM enabled in the kernel this takes > > approximately 1.5 seconds. Without HIMEM it takes 0.03 seconds. The > > time is 100% CPU and no I/O operations are done to disk. "time" reports > > there are 460 "minor" page faults with zero "major" page faults. > > I believe the issue here is the mapping of pages between high-mem and > > lowmem in the kernel paging code. This increase in time for directory > > accesses doubles to triples times for applications using samba. > > I have also tested this on another system which had only 512Meg of RAM > > but with HIMEM set in the kernel and did not experience the problem. > > I believe it only effects the performance when the paging buffers end > > up in highmem. > > > > 3. Keywords: HIMEM, Performance > > > Would you be running these in a gnome-terminal, I remember seeing a thread > that discussed gnome-terminal problems though a quick search did not turn > anything up. Here is what I get between a xterm and gnome-terminal. > > xterm > # time ls -lR /etc > real 0m0.381s > user 0m0.056s > sys 0m0.130s > > gnome-terminal > # time ls -lR /etc > real 0m0.869s > user 0m0.057s > sys 0m0.141s > > I ran this twice in both teminals and reported the > second result. > > system info > P4 3.06 HT > 2.6.7 SMP/SMT/HIGHMEM > 1GB ram > > ------------------------------------------------- > Darren Williams <dsw AT gelato.unsw.edu.au> > Gelato@UNSW <www.gelato.unsw.edu.au> > --------------------------------------------------
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