Hi all, This is a resubmit of the patch proposed by Ingo and me few month ago: http://lkml.org/lkml/2007/11/20/343 It was in -mm for a while and then removed due to a move into the mainline, but it never appeared in it. As recently a new discussion started on the subject I decided to resubmit it again. Now it is against 2.6.25.4, but as far as there are no changes in the modified files it should apply to 2.6.26-rc4 too. Comments/critics are wellcome. Marin Mitov Signed-off-by: Marin Mitov <mitov@xxxxxxxxxxx> Signed-off-by: Ingo Molnar <mingo@xxxxxxx> ========================================= --- a/arch/x86/lib/delay_32.c 2007-11-18 08:14:05.000000000 +0200 +++ b/arch/x86/lib/delay_32.c 2007-11-20 19:03:52.000000000 +0200 @@ -40,18 +40,42 @@ :"0" (loops)); } -/* TSC based delay: */ +/* TSC based delay: + * + * We are careful about preemption as TSC's are per-CPU. + */ static void delay_tsc(unsigned long loops) { - unsigned long bclock, now; + unsigned prev, prev_1, now; + unsigned left = loops; + unsigned prev_cpu, cpu; + + preempt_disable(); + rdtscl(prev); + prev_cpu = smp_processor_id(); + preempt_enable(); + now = prev; - preempt_disable(); /* TSC's are per-cpu */ - rdtscl(bclock); do { rep_nop(); + + left -= now - prev; + prev = now; + + preempt_disable(); + rdtscl(prev_1); + cpu = smp_processor_id(); rdtscl(now); - } while ((now-bclock) < loops); - preempt_enable(); + preempt_enable(); + + if (prev_cpu != cpu) { + /* + * We have migrated, forget prev_cpu's tsc reading + */ + prev = prev_1; + prev_cpu = cpu; + } + } while ((now-prev) < left); } /* --- a/arch/x86/lib/delay_64.c 2007-11-18 08:14:40.000000000 +0200 +++ b/arch/x86/lib/delay_64.c 2007-11-20 19:47:29.000000000 +0200 @@ -28,18 +28,42 @@ return 0; } +/* TSC based delay: + * + * We are careful about preemption as TSC's are per-CPU. + */ void __delay(unsigned long loops) { - unsigned bclock, now; + unsigned prev, prev_1, now; + unsigned left = loops; + unsigned prev_cpu, cpu; + + preempt_disable(); + rdtscl(prev); + prev_cpu = smp_processor_id(); + preempt_enable(); + now = prev; - preempt_disable(); /* TSC's are pre-cpu */ - rdtscl(bclock); do { - rep_nop(); + rep_nop(); + + left -= now - prev; + prev = now; + + preempt_disable(); + rdtscl(prev_1); + cpu = smp_processor_id(); rdtscl(now); - } - while ((now-bclock) < loops); - preempt_enable(); + preempt_enable(); + + if (prev_cpu != cpu) { + /* + * We have migrated, forget prev_cpu's tsc reading + */ + prev = prev_1; + prev_cpu = cpu; + } + } while ((now-prev) < left); } EXPORT_SYMBOL(__delay); - -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
