Date: Mon, 03 Mar 2008 23:19:08 +0100 From: Kris Kennaway <kris@FreeBSD.org> To: Bakul Shah <bakul@bitblocks.com> Cc: gnn@freebsd.org, current@freebsd.org Subject: Re: Differences in malloc between 6 and 7? Message-ID: <47CC795C.9050600@FreeBSD.org> In-Reply-To: <20080303211731.D89A05B30@mail.bitblocks.com> References: <20080303211731.D89A05B30@mail.bitblocks.com>
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Bakul Shah wrote: > On Mon, 03 Mar 2008 15:23:33 EST gnn@freebsd.org wrote: >> One of the folks I'm working with found this. The following code, >> which yes, is just an example, is 1/2 as fast on 7.0-RELEASE as on >> 6.3. Where should I look to find out why? > > Specifying malloc option K (double virtual memory chunk size) > roughly halves the runtime. Additional Ks reduce it more and > more. As this test spends most of its time in the kernel, > may be this is just due to the mmap overhead? Or may be the > defaults for 6.3 were different. Well, the whole architecture of malloc is different. I also see a big performance cliff (drops by a factor of 10) when malloc size exceeds the chunk size (1MB by default). Also concurrent access to mmapped memory performs badly in FreeBSD right now. I have patches that convert the vm_map lock to a sx to avoid this contention, but they need some more work. Kris
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