Messages in this thread | | | From | dr john halewood <> | Subject | Performance halved with SP APIC: 2.3.40-7 | Date | Mon, 21 Feb 2000 16:41:30 +0000 |
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problem: performance gets roughly halved on a single processor box when CONFIG_X86_UP_IOAPIC is enabled.
hardware: compaq deskpro. 400MHz PII/64Mb RAM/Intel PIIX4 controller, eepro100 network card.
Enabling APIC on single processor boxes seems to roughly halve the performance: this isn't benchmark rates, but real world applications, e.g. the following from /usr/bin/time: 2.3.42 without APIC Command being timed: "bunzip2 tmp.tar.bz2" User time (seconds): 17.86 System time (seconds): 0.21 Percent of CPU this job got: 99% Elapsed (wall clock) time (h:mm:ss or m:ss): 0:18.09 Major (requiring I/O) page faults: 102 Minor (reclaiming a frame) page faults: 911 Page size (bytes): 4096 2.3.42 with APIC Command being timed: "bunzip2 tmp.tar.bz2" User time (seconds): 37.80 System time (seconds): 0.42 Percent of CPU this job got: 196% Elapsed (wall clock) time (h:mm:ss or m:ss): 0:19.49 Major (requiring I/O) page faults: 534 Minor (reclaiming a frame) page faults: 911
(bits snipped that didn't change). Note that the number of major page faults has jumped massively (and the wall clock time was completely wrong). I've also noticed that /proc/interrupts shows that the number of interrupts on IRQ 11 (usb-uhci & ethernet) seems much higher with APIC enabled. Can't see any immediate fix, apart from a change to the config menu to put a warning and maybe remove the comment "Such a kernel will still boot on IO-APIC-less sstems with no slowdown at all."
I've got a feeling this is more to do with educating people like me who tend to select 'y' for anything they've not tried before than actually being a bug but it's probably worth clarifying.
cheers john
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