Date: Thu, 24 Apr 2003 19:35:36 +0200 (CEST) From: Michal Mertl <mime@traveller.cz> To: vizion communication <vizion@ixpres.com> Cc: freebsd-smp@freebsd.org Subject: Re: Anyone please???? SMP health check!! Message-ID: <20030424191157.Q55270@prg.traveller.cz> In-Reply-To: <00a901c30a64$c8101390$15b55042@vizion2000.net> References: <004e01c30a16$73999870$15b55042@vizion2000.net> <00a901c30a64$c8101390$15b55042@vizion2000.net>
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> Thanks very much for your comments -- they are really > appreciated. > > OK is there any way I can check that SMP is performing > properly?? You should see 8th column in top labeled C which shows on which processor given process runs. > I do not seem to be showing an increase in performance > between single and smp processing. SMP performs better only for some tasks. With some kind of load you can get even worse performance than with UP kernel. The reason is that with SMP kernel the kernel itself runs at any given moment only on one processor. User level processing can run at the same time on other ones though. With lots of user level processing you should see much higher performance on SMP - try running dnetc or setiathome. It shows almost linear increase in performance with added processors. If your load in mostly in kernel (be it disk / network I/O, number of syscalls or whatever) you wouldn't see much of an improvement, in rare cases even a slowdown caused by more complex locking with SMP kernel. There's another problem with SMP on 4.X and that's with multi-threaded applications. libc_r library, which provides native FreeBSD threads on 4.X, can run only one thread at a time (runs all thread on the same processor). What's also bad (I'm not 100% sure about this one) is that whenever one thread blocks (e.g. wants disk I/O) the whole application blocks. So for some threaded applications (e.g. mysql) you should see better performance with linuxthreads port which basically turns threads into processes. You can then run more threads at the same time and the blocking problem shouldn't occur either. > What issues would not be revealed in Dmesg? Don't know of any. If you see 'SMP: AP CPU #1 Launched!' in means the system will be able to use second processor. For the error (warning) message you got I thought if the system continued booting it shouldn't be that bad. I seem to remember, that some warnings like this affect performance though. I've got a lot of SMP FreeBSD installations with different HW. I don't get any warnings with 440BX based boards but get some with ServerWorks boards (Xeon P4 and PIII). Mostly the following one, but I think I saw some other on some of my systems. APIC_IO: Testing 8254 interrupt delivery APIC_IO: Broken MP table detected: 8254 is not connected to IOAPIC #0 intpin 2 APIC_IO: routing 8254 via 8259 and IOAPIC #0 intpin 0 -- Michal Mertl mime@traveller.cz
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