On Tue, 22 May 2001, null wrote: > Here is some additional info about the 2.4 performance defect. > > Only one person offered a suggestion about the use of HIGHMEM. I tried > with and without HIGHMEM enabled with the same results. However, it does > appear to take a bit longer to reach performance drop-out condition when > HIGHMEM is disabled. > > The same system degradation also appears when using partitions on a single > internal SCSI drive, but seems to happen only when performing the I/O in > parallel processes. It appears that the load must be sustained long > enough to affect some buffer cache behavior. Parallel dd commands > (if=/dev/zero) also reveal the problem. I still need to do some > benchmarks, but it looks like 2.4 kernels achieve roughly 25% (or less?) > of the throughput of the 2.2 kernels under heavy parallel loads (on > identical hardware). I've also confirmed the defect on a dual-processor > Xeon system with 2.4. The defect exists whether drivers are built-in or > compiled as modules, altho the parallel mkfs test duration improves by as > much as 50% in some cases when using a kernel with built-in SCSI drivers. That's a very interesting observation. May I suggest that the problem may be the driver for your SCSI device? I just ran some tests of parallel I/O on a 2 CPU Intel Pentium III 800 MHz with 2GB main memory, on a single Seagate Barracuda ST336704LWV attached to a AIC7896. The system controller is Intel 440GX. The kernel is 2.4.3-ac7: jwb@windmill:~$ for i in 1 2 3 4 5 6 7 8 9 10; do time dd if=/dev/zero of=/tmp/$i bs=4096 count=25600 & done; This spawns 10 writers of 100MB files on the same filesystem. While all this went on, the system was responsive, and vmstat showed a steady block write of at least 20000 blocks/second. Meanwhile this machine also has constantly used mysql and postgresql database systems and a few interactive users. The test completed in 19 seconds and 24 seconds on separate runs. I also performed this test on a machine with 2 Intel Pentium III 933 MHz CPUs, 512MB main memory, an Intel 840 system controller, and a Quantum 10K II 9GB drive attached to an Adaptec 7899P controller, using kernel 2.4.4-ac8. I had no problems there either, and the test completed in 30 seconds (with a nearly full disk). I also didn't see this problem on an Apple Powerbook G4 nor on another Intel machine with a DAC960 RAID. In short, I'm not seeing this problem. Regards, Jeffrey Baker - 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/
