linux-kernel - Re: [v2 0/5] parallelized "struct page" zeroing

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Message-ID: <20170325212558.GA1288@bombadil.infradead.org>
Date:   Sat, 25 Mar 2017 14:25:58 -0700
From:   Matthew Wilcox <willy@...radead.org>
To:     Pavel Tatashin <pasha.tatashin@...cle.com>
Cc:     linux-kernel@...r.kernel.org, sparclinux@...r.kernel.org,
        linux-mm@...ck.org, linuxppc-dev@...ts.ozlabs.org,
        linux-s390@...r.kernel.org, borntraeger@...ibm.com,
        heiko.carstens@...ibm.com, davem@...emloft.net
Subject: Re: [v2 0/5] parallelized "struct page" zeroing

On Fri, Mar 24, 2017 at 03:19:47PM -0400, Pavel Tatashin wrote:
> Changelog:
> 	v1 - v2
> 	- Per request, added s390 to deferred "struct page" zeroing
> 	- Collected performance data on x86 which proofs the importance to
> 	  keep memset() as prefetch (see below).
> 
> When deferred struct page initialization feature is enabled, we get a
> performance gain of initializing vmemmap in parallel after other CPUs are
> started. However, we still zero the memory for vmemmap using one boot CPU.
> This patch-set fixes the memset-zeroing limitation by deferring it as well.
> 
> Performance gain on SPARC with 32T:
> base:	https://hastebin.com/ozanelatat.go
> fix:	https://hastebin.com/utonawukof.go
> 
> As you can see without the fix it takes: 97.89s to boot
> With the fix it takes: 46.91 to boot.
> 
> Performance gain on x86 with 1T:
> base:	https://hastebin.com/uvifasohon.pas
> fix:	https://hastebin.com/anodiqaguj.pas
> 
> On Intel we save 10.66s/T while on SPARC we save 1.59s/T. Intel has
> twice as many pages, and also fewer nodes than SPARC (sparc 32 nodes, vs.
> intel 8 nodes).
> 
> It takes one thread 11.25s to zero vmemmap on Intel for 1T, so it should
> take additional 11.25 / 8 = 1.4s  (this machine has 8 nodes) per node to
> initialize the memory, but it takes only additional 0.456s per node, which
> means on Intel we also benefit from having memset() and initializing all
> other fields in one place.

My question was how long it takes if you memset in neither place.