Leon wrote:
I hope the OpenSSL maintainers heard this cry (even if it is a small
cry) and will at some point decide to use a better method than select.
This got patched in CVS yesterday for Linux.
David Schwartz wrote:
A patch to use 'poll' instead of 'select' where it's available would be
a
very good idea. Using 'select' to check readiness of a single descriptor
that you just opened is about the worst-case scenario for 'select' (because
it has to scan through all the unset bits on each set). Using 'poll' is far
more efficient for a single descriptor since no scanning is needed.
The performance of finding the first set bit from a 128byte block of
data really isn't that bad inside the kernel. Faster than a strcpy() of
a 128byte string I'd say, as there is no memory writing going on. Its
also probably still in CPU the cache as your just did FD_ZERO()/FD_SET()
on it.
A number of CPUs support assembly instructions to facilitate it and
operate on 32bit/64bit slices. How would file system free block bitmaps
get on is there was something really bad about it.
linux/include/asm-i386/bitops.h: find_first_bit() uses i386 BSF.
Its probably not used in the kernel for the select() syscall as its
converted to poll() and I guess for most general usage of select on many
fds there are more bits set than not set in the range provided.
Darryl
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