linux-kernel - [RFC 0/4]x86: allocate up to 32 tlb invalidate vectors

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Message-ID: <1288766655.23014.113.camel@sli10-conroe>
Date:	Wed, 03 Nov 2010 14:44:15 +0800
From:	Shaohua Li <shaohua.li@...el.com>
To:	lkml <linux-kernel@...r.kernel.org>
Cc:	Ingo Molnar <mingo@...e.hu>, Andi Kleen <andi@...stfloor.org>,
	"hpa@...or.com" <hpa@...or.com>
Subject: [RFC 0/4]x86: allocate up to 32 tlb invalidate vectors

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

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