Sonny Rao a écrit :
On Mon, Sep 12, 2005 at 08:34:17PM -0700, Linus Torvalds wrote:
<snip>
On the filesystem level, FUSE got merged, and ntfs and xfs got updated. In
the core VFS layer, the "struct files" thing is now handled with RCU and
has less expensive locking.
I hope this means that people will be more accepting of multi-threaded
benchmarks (who needs real apps... ;-)) which do open() and close().
Yes, no?
If you look at RCU change, you discover they impact read()/write()/... (no
more locking), but not open()/dup()/socket() and close() that still take a
spinlock to modify the state.
And if your process has many files opened, the cost (read : latency) of open()
can be very high, finding a zero bit in a large bit array.
So these RCU changes can help some benchmarks (or real apps... ;-) ), but not
some others :)
I wish a process param could allow open() to take any free fd available, not
the lowest one. One can always use fcntl(fd, F_DUPFD, slot) to move a fd on a
specific high slot and always keep the 64 first fd slots free to speedup the
kernel part at open()/dup()/socket() time.
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