Tejun Heo wrote:
Other than local_bh_disable/enable(), all brsem read ops do are
1. accessing sem->idx
2. calculate per-cpu rcnt address from sem->idx
3. do one branch on the value of per-cpu rcnt
4. inc/dec per-cpu rcnt
So, it does access one more cachline and, yeap, there is one branch for
bh enabling and several more inside local_bh_enable. I'll try to get
some benchmark numbers for comparison.
Well local_bh_disable touches the preempt count too, although we
can probably assume that's hot in cache.
You might also find yours has a bigger icache footprint as well.
I'm thinking about adding down_read(&xxx->s_umount) to write(2) and
compare normal rwsem and brsem performance by repeitively writing short
data into a file on a UP machine. Do you have better ideas?
To be honest I'd say that you wouldn't be able to measure it if
you're going through a regular system call path, although such
a measurement certainly won't hurt.
I don't have a better idea though. I don't think a busy loop
microbenchmark is going to be very informative either, it might
actually give a measurable difference but that difference
probably won't be too representitive of real use :\
--
SUSE Labs, Novell Inc.
Send instant messages to your online friends http://au.messenger.yahoo.com
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
| |
 |