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

george anzinger
2003-03-19T02:12:10Z

H. Peter Anvin wrote:
> Followup to: <Pine.LNX.4.44.0303181113590.13708-100000@home.transmeta.com>
> By author: Linus Torvalds <torvalds@transmeta.com>
> In newsgroup: linux.dev.kernel
>
>>Wow. There aren't many things that AMD tends to show the P4-like "big
>>latency in rare cases" behaviour.
>>
>>But quite honestly, I think they made the right call, and I _expect_ that
>>of modern CPU's. The fact is, modern CPU's tend to need to pre-decode the
>>instruction stream some way, and storing to it while running from it is
>>just a really really bad idea. And since it's so easy to avoid it, you
>>really just shouldn't do it.
>>
>
>
> AMD, I believe, has an "annotated" icache

Here is an SMP:

vendor_id : AuthenticAMD
cpu family : 6
model : 6
model name : AMD Athlon(TM) MP 2000+
stepping : 2
cpu MHz : 1680.368
cache size : 256 KB

empty overhead=11 cycles
load overhead=6 cycles
I$ load overhead=5 cycles
I$ load overhead=6 cycles
I$ store overhead=1051 cycles

--
George Anzinger george@mvista.com
High-res-timers: http://sourceforge.net/projects/high-res-timers/
Preemption patch: http://www.kernel.org/pub/linux/kernel/people/rml