Re: [RFC][PATCH] flush_icache_user_range

[Andrea Arcangeli]

On Thu, Nov 22, 2001 at 07:48:28PM +0100, Andrea Arcangeli wrote:
> On Thu, Nov 22, 2001 at 10:43:48PM +1100, Paul Mackerras wrote:
> > The patch below changes access_one_page in kernel/ptrace.c to use a
> > new function, flush_icache_user_range, instead of flush_icache_page as
> > at present.  The reason for making this change is that
> > flush_icache_page is also called in do_no_page and do_swap_page, where
> > it does a fundamentally different job.  Decoupling the two makes it
> > possible to improve performance, because we can make flush_icache_page
> > do the flush only when needed.
> > 
> > This patch particularly affects alpha: for alpha I renamed the
> > existing flush_icache_page to flush_icache_user_range and made
> > flush_icache_page a no-op.  This is based on a suggestion from
> > Andrea and the comments in the code.  I would be very interested to
> > hear how it affects alpha as regards stability and performance.
> > 
> > For PPC, I have added a flush_icache_user_range that only flushes the
> > cachelines that have been modified.  I have a more extensive
> > cache-flush avoidance patch in the works that depends on this one and
> > also needs modifications to clear_user_page and copy_user_page.  This
> > all gives us a substantial performance increase on PPC.
> > 
> > For all the other architectures I have made flush_icache_user_range
> > the same as flush_icache_page, i.e. a no-op for most architectures.
> > So this patch should have zero impact except on alpha and PPC, and on
> > alpha it should improve performance.
> > 
> > Note that flush_icache_user_range is different from flush_icache_page
> > now in that flush_icache_user_range is only called when the page has
> > been modified, so we know we do have to flush (if the icache doesn't
> > snoop stores by the cpu).  In contrast, flush_icache_page is called in
> > situations where the page often (usually?) is unmodified, so it makes
> > sense to try to work out whether the flush is actually needed.
> > 
> > Comments?  Linus, would you be willing to apply this?
> 
> I will try to give it a spin, it should be a very nice speedup for

it seems to work fine on my dual ev6.

Andrea