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From: David Mosberger <davidm@napali.hpl.hp.com>
Somebody recently pointed out a performance-anomaly to me where an unusual
amount of time was being spent reading from /dev/urandom. The problem
isn't really surprising as it happened only on >= 4-way machines and the
random driver isn't terribly scalable the way it is written today. If
scalability _really_ mattered, I suppose per-CPU data structures would be
the way to go. However, I found that at least for 4-way machines,
performance can be improved considerably with the attached patch. In
particular, I saw the following performance on a 4-way ia64 machine:
Test: 3 tasks running "dd if=/dev/urandom of=/dev/null bs=1024":
throughput:
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include/linux/prefetch.h does a strange thing: if the arch doesn't have
the prefectch functions, this header defines no-op version of them and
then defines ARCH_HAS_PREFETCH. So there's no way for mainline code to
know if the architecture *really* has prefetch instructions.
This information loss is unfortunate. Examples:
for (i = 0; i < N; i++)
prefetch(foo[i]);
Problem is, if `prefetch' is a no-op, the compiler will still
generate an empty busy-wait loop. Which it must do. We need to
know the truth about ARCH_HAS_PREFETCH to correctly elide that loop.
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- Alan Cox: much more merging
- Pete Zaitcev: ymfpci race fixes
- Andrea Arkangeli: VM race fix and OOM tweak.
- Arjan Van de Ven: merge RH kernel fixes
- Andi Kleen: use more readable 'likely()/unlikely()' instead of __builtin_expect()
- Keith Owens: fix 64-bit ELF types
- Gerd Knorr: mark more broken PCI bridges, update btaudio driver
- Paul Mackerras: powermac driver update
- me: clean up PTRACE_DETACH to use common infrastructure
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- Merge with Alan
- Trond Myklebust: NFS fixes - kmap and root inode special case
- Al Viro: more superblock cleanups, inode leak in rd.c, minix
directories in page cache
- Paul Mackerras: clean up rubbish from sl82c105.c
- Neil Brown: md/raid cleanups, NFS filehandles
- Johannes Erdfelt: USB update (usb-2.0 support, visor fix, Clie fix,
pl2303 driver update)
- David Miller: sparc and net update
- Eric Biederman: simplify and correct bootdata allocation - don't
overwrite ramdisks
- Tim Waugh: support multiple SuperIO devices, parport doc updates
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