Date: Thu, 05 Jan 2012 12:46:24 -0500 From: "Dieter BSD" <dieterbsd@engineer.com> To: freebsd-performance@freebsd.org Subject: Re: cmp(1) has a bottleneck, but where? Message-ID: <20120105174626.218240@gmx.com>
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> Something/somehow it's issuing smaller IOs when using mmap? On my box, 64K reads. Using the '-' to avoid mmap it uses 128K. The big difference I found was that the default mmap case isn't using read-ahead. So it has to wait on the disk every time. :-( Using the '-' to avoid mmap it benefits from read-ahead, but the default of 8 isn't large enough. Crank up vfs.read_max and it becomes cpu bound. (assuming using 2 disks and not limited by both disks being on the same wimpy controller) A) Should the default vfs.read_max be increased? B) Can the mmap case be fixed? What is the aledged benefit of using mmap anyway? All I've even seen are problems.home | help
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