Ravikiran G Thirumalai <[EMAIL PROTECTED]> wrote: > > On Fri, Jan 27, 2006 at 03:01:06PM -0800, Andrew Morton wrote: > > Ravikiran G Thirumalai <[EMAIL PROTECTED]> wrote: > > > > > > > > > > > > If the benchmarks say that we need to. If we cannot observe any > > > > problems > > > > in testing of existing code and if we can't demonstrate any benefit from > > > > the patched code then one option is to go off and do something else ;) > > > > > > We first tried plain per-CPU counters for memory_allocated, found that > > > reads > > > on memory_allocated was causing cacheline transfers, and then > > > switched over to batching. So batching reads is useful. To avoid > > > inaccuracy, we can maybe change percpu_counter_init to: > > > > > > void percpu_counter_init(struct percpu_counter *fbc, int maxdev) > > > > > > the percpu batching limit would then be maxdev/num_possible_cpus. One > > > would > > > use batching counters only when both reads and writes are frequent. With > > > the above scheme, we would go fetch cachelines from other cpus for read > > > often only on large cpu counts, which is not any worse than the global > > > counter alternative, but it would still be beneficial on smaller machines, > > > without sacrificing a pre-set deviation. > > > > > > Comments? > > > > Sounds sane. > > > > Here's an implementation which delegates tuning of batching to the user. We > don't really need local_t at all as percpu_counter_mod is not safe against > interrupts and softirqs as it is. If we have a counter which could be > modified in process context and irq/bh context, we just have to use a > wrapper like percpu_counter_mod_bh which will just disable and enable bottom > halves. Reads on the counters are safe as they are atomic_reads, and the > cpu local variables are always accessed by that cpu only. > > (PS: the maxerr for ext2/ext3 is just guesstimate)
Well that's the problem. We need to choose production-quality values for use in there. > Comments? Using num_possible_cpus() in that header file is just asking for build errors. Probably best to uninline the function rather than adding the needed include of cpumask.h. - To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html
