Re: [Bug 350] New: i386 context switch very slow compared to 2.4 due to wrmsr (performance)

Linus Torvalds
2003-03-10T02:59:03Z

Ok Jamie,
since you've been interested in the past, I thought I'd ask you to test
the current context switch stuff. Andi cleaned up some FPU reload stuff
(and I fixed a bug in it, tssk tssk Andi - you'd obviously not actually
timed your cleanups), and I just committed and pushed out my "cache the
value of SYSENTER_CS in the TSS" patch.

It won't bring context switching back to where it _could_ be, but it
should be noticeably better. My pipe bandwidth is up from under 600MB/s
to about ~700MB/s according to lmbench.

Your SYSENTER_ESP hack would probably get back the rest, but I haven't
seen any patches for it, hint hint.

In the meantime, we're almost back to where we were _and_ we support
sysenter (ie my system calls are down by almost a factor of four). So
we're doing pretty well.

Linus