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

[Kaushik Kumar Ram <kaushik@xxxxxxxx>]

On Jan 31, 2010, at 2:24 AM, Keir Fraser wrote:

> 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?

OK. I will give it a shot.

-Kaushik
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