[PATCH 0/4]x86: allocate up to 32 tlb invalidate vectors -resend

[PATCH 0/4]x86: allocate up to 32 tlb invalidate vectors -resend

[Shaohua Li]

last post is lost, resent.

Hi,
In workload with heavy page reclaim, flush_tlb_page() is frequently
used. We currently have 8 vectors for tlb flush, which is fine for small
machines. But for big machines with a lot of CPUs, the 8 vectors are
shared by all CPUs and we need lock to protect them. This will cause a
lot of lock contentions. please see the patch 3 for detailed number of
the lock contention.
Andi Kleen suggests we can use 32 vectors for tlb flush, which should be
fine for even 8 socket machines. Test shows this reduces lock contention
dramatically (see patch 3 for number).
One might argue if this will waste too many vectors and leave less
vectors for devices. This could be a problem. But even we use 32
vectors, we still leave 78 vectors for devices. And we now have per-cpu
vector, vector isn't scarce any more, but I'm open if anybody has
objections.

Thanks,
Shaohua

Re: [PATCH 0/4]x86: allocate up to 32 tlb invalidate vectors -resend

[Shaohua Li]

On Mon, 2011-01-17 at 10:51 +0800, Shaohua Li wrote:
> last post is lost, resent.
> 
> Hi,
> In workload with heavy page reclaim, flush_tlb_page() is frequently
> used. We currently have 8 vectors for tlb flush, which is fine for small
> machines. But for big machines with a lot of CPUs, the 8 vectors are
> shared by all CPUs and we need lock to protect them. This will cause a
> lot of lock contentions. please see the patch 3 for detailed number of
> the lock contention.
> Andi Kleen suggests we can use 32 vectors for tlb flush, which should be
> fine for even 8 socket machines. Test shows this reduces lock contention
> dramatically (see patch 3 for number).
> One might argue if this will waste too many vectors and leave less
> vectors for devices. This could be a problem. But even we use 32
> vectors, we still leave 78 vectors for devices. And we now have per-cpu
> vector, vector isn't scarce any more, but I'm open if anybody has
> objections.
any comments on this patch set?

Thanks,
Shaohua