lkml.org 
[lkml]   [2012]   [Jul]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH RFC 0/2] kvm: Improving directed yield in PLE handler
On 09/07/12 08:20, Raghavendra K T wrote:
> Currently Pause Looop Exit (PLE) handler is doing directed yield to a
> random VCPU on PL exit. Though we already have filtering while choosing
> the candidate to yield_to, we can do better.
>
> Problem is, for large vcpu guests, we have more probability of yielding
> to a bad vcpu. We are not able to prevent directed yield to same guy who
> has done PL exit recently, who perhaps spins again and wastes CPU.
>
> Fix that by keeping track of who has done PL exit. So The Algorithm in series
> give chance to a VCPU which has:


We could do the same for s390. The appropriate exit would be diag44 (yield to hypervisor).

Almost all s390 kernels use diag9c (directed yield to a given guest cpu) for spinlocks, though.
So there is no win here, but there are other cases were diag44 is used, e.g. cpu_relax.
I have to double check with others, if these cases are critical, but for now, it seems
that your dummy implementation for s390 is just fine. After all it is a no-op until
we implement something.

Thanks

Christian



\
 
 \ /
  Last update: 2012-07-09 10:21    [W:0.245 / U:0.100 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site