Re: [Xen-devel] [PATCH] evtchn_do_upcall: search a snapshot of level 2 bits for pending upcalls

[Keir Fraser <keir.fraser@xxxxxxxxxxxxx>]

On 31/01/2010 00:40, "Kaushik Kumar Ram" <kaushik@xxxxxxxx> wrote:

>> So how about making the clear of l1i in the l1 mask unconditional? I think
>> that would be better, but I wasn't sure it is safe, since the first l1i you
>> scan you may start halfway through, and thus legitimately have more work to
>> do on that l1i on a later iteration of the outer loop. But I think that is
>> the only case it is good to leave the l1 unmasked? Also, even better, on
>> that second scan of that l1i, you would preferably want to scan only those
>> bits in the l2 mask that you didn't scan on the first iteration of the outer
>> loop!
> 
> OK. I agree the following is a good compromise.
> - Unconditionally clear l1 bits except the first l1i (but only if l2 is
> scanned from halfway).
> - Remember where the scanning began (both l1i and l2i) and stop scanning at
> that point after wrapping around.
> - Read active_evtchns() once per l1i (except the first l1i where you might
> have to do it twice).

Yes, sounds good. Are you going to make the patch?

 -- Keir



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