Brett Glass wrote:
I will need to build several Web caches over the next few months, and
just took advantage of the Christmas lull (and a snowy day, when I
couldn't work outside) to test FreeBSD 7.0 BETA 4 to see how it will
perform at this task. I built up a 4 core FreeBSD box, and asked a
friend who's a Linux fanatic to do the same with Linux on identical
hardware. I didn't watch closely how he installed everything, but asked
him not to tune it beyond setting it up properly for SMP.
We then ran a test suite in which a client starts several processes.
Each uses wget to fetch a series of objects in rapid succession via the
cache. The fetches done by each process are the same batch of URLS, but
shuffled differently, so each URL will get a miss the first time and
then hits each time it comes up thereafter unless the cache overflows.
We're doing all GETs, with no tricky stuff like subranges.
As has been reported in some other messages on this list, Linux is
currently blowing FreeBSD away. It's taking as much as 20% less time to
get through the benchmark, depending on exactly how the random shuffle
came out. This is with 4 GB RAM, the GENERIC FreeBSD SMP kernel (using
SCHED_ULE), and aufs as the storage schema for Squid.
It appears, though I'd need to instrument the code more to be sure, that
the slowdown is coming from file I/O. Could it be that there less
concurrency or more overhead in FreeBSD file operations than there is in
Linux? Even with SoftUpdates turned on, the cache volume mounted with
-noatime, and aufs (which uses kqueues -- a FreeBSD invention -- to
optimize multithreaded disk access), the benchmark shows FreeBSD losing
out. Why?
Brett,
There could be several problems here:
1. WITNESS, INVARIANTS, malloc debugging. Are any of these turned on
for you? I don't recall if malloc debugging got turned off yet for the
7.0 snapshots.
2. Disk subsystem. What kind of disk controller are you using? Not all
drivers work well in FreeBSD. Are linux and freebsd using identical
hardware?
3. Directory hashing. If you're using squid, you __must__ tune the
DIRHASH, otherwise you'll spend a lot of time doing pathname lookups.
What filesystem is linux using?
Would you mind if I logged into your test system and looked around to
help diagnose the problem?
Scott
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