kvm_read() vs ioctl performance
phk at phk.freebsd.dk
Sat Mar 22 06:32:23 PDT 2008
In message <416202.18656.qm at web63914.mail.re1.yahoo.com>, Barney Cordoba writes
>I can't easily follow this driver, given the superior
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 at 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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