On 05/03/2025 11:36 am, Jan Beulich wrote:
> On 05.03.2025 00:22, Andrew Cooper wrote:
>> There are two issues. First, pi_test_and_clear_on() pulls the cache-line to
>> the CPU and dirties it even if there's nothing outstanding, but the final
>> bitmap_for_each() is O(256) when O(8) would do, and would avoid multiple
>> atomic updates to the same IRR word.
>>
>> Rewrite it from scratch, explaining what's going on at each step.
>>
>> Bloat-o-meter reports 177 -> 145 (net -32), but real improvement is the
>> removal of calls to __find_{first,next}_bit() hidden behind
>> bitmap_for_each().
> Nit: As said in reply to v2, there are no underscores on the two find
> functions bitmap_for_each() uses.
I did change the commit message assuming you were right, but the
disassembly never lies.
What bitmap_for_each() uses are very much not functions in x86.
>> No functional change.
>>
>> Signed-off-by: Andrew Cooper <[email protected]>
>> ---
>> CC: Jan Beulich <[email protected]>
>> CC: Roger Pau Monné <[email protected]>
>>
>> https://gitlab.com/xen-project/people/andyhhp/xen/-/pipelines/1699791518
>>
>> v3:
>> * Fix IRR scatter address calculation
>> * Spelling/Grammar improvements
> The description starting with "There are two issues" I fear it still
> doesn't become quite clear what the 2nd issue is. I can only assume it's
> the use of bitmap_for_each() that now goes away.
>
> Preferably with this tweaked a little further
> Reviewed-by: Jan Beulich <[email protected]>
Oh. ", but the final" can turn into ", and second,". That should make
it clearer.
Thanks,
~Andrew
