Date: Sat, 22 Mar 2008 13:32:21 +0000 From: "Poul-Henning Kamp" <phk@phk.freebsd.dk> To: Barney Cordoba <barney_cordoba@yahoo.com> Cc: Julian Elischer <julian@elischer.org>, current@freebsd.org Subject: Re: kvm_read() vs ioctl performance Message-ID: <11008.1206192741@critter.freebsd.dk> In-Reply-To: Your message of "Sat, 22 Mar 2008 06:26:46 MST." <416202.18656.qm@web63914.mail.re1.yahoo.com>
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In message <416202.18656.qm@web63914.mail.re1.yahoo.com>, Barney Cordoba writes : >I can't easily follow this driver, given the superior >comments :) Look at the mmap() function. >My concern is this: stats may be updated in iterations >of 100K+ times per second, while stats are only >gathered once every few seconds. Even a tiny addition >to the kernel cpu cycles can make it a "cut off your >head to stop a nosebleed" scenario. I don't want to >lose cpu cycles for the sake of saving a fraction of a >ms every few minutes. The point about using shared memory, is that it is just that: shared memory. The memory the kernel writes to, is the same memory the userland reads from. There is _no_ overhead anywhere. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 phk@FreeBSD.ORG | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence.
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