Messages in this thread | | | Date | Thu, 11 Sep 2003 16:32:48 +0200 | From | Andi Kleen <> | Subject | Re: [PATCH] 2.6 workaround for Athlon/Opteron prefetch errata |
| |
On Thu, 11 Sep 2003 15:28:09 +0100 Dave Jones <davej@redhat.com> wrote:
> On Thu, Sep 11, 2003 at 04:24:21PM +0200, Andi Kleen wrote: > > I considered that when writing the patch, but: is_prefetch is a single byte > > memory access for something already in cache. Checking for an Athlon > > CPU needs two memory accesses in boot_cpu_data at least (checking vendor > > and model) > > You only need to check it once when the path is first taken, and then > set a variable that makes you exit as soon as you enter it again.
Checking the variable also an memory access.
is_prefetch does a few more instructions around the memory access, but these are completely left in the noise.
The is_prefetch check is likely faster even than checking that variable because the chances that the EIP is already in cache are much higher than some rarely used variable.
-Andi - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |