Messages in this thread | | | From | Rusty Russell <> | Subject | Re: [PATCH] In-kernel module loader 3/7 | Date | Thu, 19 Sep 2002 12:05:05 +1000 |
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In message <Pine.LNX.4.44.0209190042370.8911-100000@serv> you write: > Hi, > > On Wed, 18 Sep 2002, Rusty Russell wrote: > > > +/* Stopping interrupts faster than atomics on many archs (and more > > + easily optimized if they're not) */ > > +static inline void bigref_inc(struct bigref *ref) > > +{ > > + unsigned long flags; > > + struct bigref_percpu *cpu; > > + > > + local_irq_save(flags); > > + cpu = &ref->ref[smp_processor_id()]; > > + if (likely(!cpu->slow_mode)) > > + cpu->counter++; > > Did you benchmark this? On most UP machines an inc/dec should be cheaper > than irq enable/disable.
Oops, I forgot to test that: I had both implementations.
Doing a million loop (so there's loop overhead):
350MHz dual Pentium II, atomic is almost twice as fast PPC 500MHz G4: atomic is 3.5 times as fast. Power3 4-way 375MHz machine: atomic is 10% faster. Power4 4-way 1.3GHz machine: atomic was 20% slower (depending on version if irq_restore).
I suspect a P4 might get similar pro-irq results (code below, anyone?)
Ideally we'd have a "local_inc()" and "local_dec()". Architectures which do soft interrupts enabling should see a real win from the save/restore version.
Meanwhile, I'll revert to atomics, since it's sometimes dramatically faster.
Thanks! Rusty. -- Anyone who quotes me in their sig is an idiot. -- Rusty Russell.
static void test(void) { struct timeval start, end; atomic_t x; unsigned int tmp, i, diff; unsigned long flags;
/* Atomic test. */ atomic_set(&x, 0); do_gettimeofday(&start); for (i = 0; i < 1000000; i++) atomic_dec(&x); do_gettimeofday(&end);
diff = (end.tv_sec - start.tv_sec) * 1000000 + (end.tv_usec - start.tv_usec); printk("Atomic test: %u usec\n", diff);
/* Interrupt test (interrupts enabled) */ tmp = 0; do_gettimeofday(&start); for (i = 0; i < 1000000; i++) { local_irq_save(flags); tmp++; local_irq_restore(flags); } do_gettimeofday(&end);
diff = (end.tv_sec - start.tv_sec) * 1000000 + (end.tv_usec - start.tv_usec); printk("Interrupt test: %u usec\n", diff);
/* Interrupt test (interrupts disabled) */ tmp = 0; local_irq_disable(); do_gettimeofday(&start); for (i = 0; i < 1000000; i++) { local_irq_save(flags); tmp++; local_irq_restore(flags); } do_gettimeofday(&end); local_irq_enable();
diff = (end.tv_sec - start.tv_sec) * 1000000 + (end.tv_usec - start.tv_usec); printk("Interrupt test (interrupts disabled): %u usec\n", diff); } - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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