Messages in this thread Patch in this message |  | | Subject | Re: [PATCH] hyperthreading scheduler improvement | From | Robert Love <> | Date | 26 Aug 2002 16:53:58 -0400 |
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On Mon, 2002-08-26 at 16:05, Robert Love wrote:
Linus,
> This patch implements a per-arch load balancing scheme for P4s to better > balance across the virtual CPUs (e.g. prefer fully unused CPUs to a > single available HT unit). This is the same logic in 2.4-ac, 2.4-aa, > etc. > > This patch uses the previously posted per-arch load balancing > infrastructure.
This is an updated version, to use the new asm/sched.h infrastructure hch suggested (see previous patch).
Robert Love
diff -urN linux-dogmeat/arch/i386/config.in linux/arch/i386/config.in --- linux-dogmeat/arch/i386/config.in Mon Aug 26 16:30:53 2002 +++ linux/arch/i386/config.in Mon Aug 26 16:45:57 2002 @@ -103,6 +103,7 @@ define_bool CONFIG_X86_TSC y define_bool CONFIG_X86_GOOD_APIC y define_bool CONFIG_X86_USE_PPRO_CHECKSUM y + define_bool CONFIG_X86_HYPERTHREADING y fi if [ "$CONFIG_MK6" = "y" ]; then define_int CONFIG_X86_L1_CACHE_SHIFT 5 diff -urN linux-dogmeat/include/asm-i386/sched.h linux/include/asm-i386/sched.h --- linux-dogmeat/include/asm-i386/sched.h Mon Aug 26 16:31:12 2002 +++ linux/include/asm-i386/sched.h Mon Aug 26 16:46:37 2002 @@ -1,7 +1,55 @@ #ifndef _I386_SCHED_H #define _I386_SCHED_H -/* nothing to see here, move along */ -#include <asm-generic/sched.h> +/* + * We have an architecture-specific SMP load balancer to improve + * scheduling behavior on hyperthreaded CPUs. Since only P4s have + * HT, we only use the code if CONFIG_MPENTIUM4 is set. + * + * Distributions may want to make this unconditional to support all + * x86 machines on one kernel. The overhead in the non-P4 case is + * minimal while the benefit to SMP P4s is probably decent. + */ +#if defined(CONFIG_X86_HYPERTHREADING) + +/* + * Find any idle processor package (i.e. both virtual processors are idle) + */ +static inline int find_idle_package(int this_cpu) +{ + int i; + + i = this_cpu; + + for (i = (this_cpu + 1) % NR_CPUS; + i != this_cpu; + i = (i + 1) % NR_CPUS) { + int sibling = cpu_sibling_map[i]; + + if (idle_cpu(i) && idle_cpu(sibling)) + return i; + } + return -1; /* not found */ +} + +static inline int arch_load_balance(int this_cpu, int idle) +{ + /* Special hack for hyperthreading */ + if (unlikely(smp_num_siblings > 1 && idle && !idle_cpu(cpu_sibling_map[this_cpu]))) { + int found; + struct runqueue *rq_target; + + if ((found = find_idle_package(this_cpu)) >= 0 ) { + rq_target = cpu_rq(found); + resched_task(rq_target->idle); + return 1; + } + } + return 0; +} + +#else +#define arch_load_balance(x, y) (0) +#endif #endif /* _I386_SCHED_H */ - 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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