Messages in this thread Patch in this message | | | Date | Tue, 20 Nov 2007 22:37:46 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] new TSC based delay_tsc() |
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hi Marin,
here's the patch we are carrying in x86.git at the moment - could you please update it with v3 of your code, and send us the patch (with the patch metadata kept intact, like you see it below)? Thanks,
Ingo
-----------------> From: Marin Mitov <mitov@issp.bas.bg> Subject: new TSC based delay_tsc()
This is a patch based on the Ingo's idea/patch to track delay_tsc() migration to another cpu by comparing smp_processor_id().
What is different: 1. Using unsigned (instead of long) to unify for i386/x86_64. 2. Minimal preempt_disable/enable() critical sections (more room for preemption) 3. some statements have been rearranged, to account for possible under/overflow of left/TSC
Tested on both: 32/64 bit SMP PREEMPT kernel-2.6.24-rc3
Signed-off-by: Marin Mitov <mitov@issp.bas.bg> Signed-off-by: Ingo Molnar <mingo@elte.hu> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> --- arch/x86/lib/delay_32.c | 35 +++++++++++++++++++++++++++++------ arch/x86/lib/delay_64.c | 36 ++++++++++++++++++++++++++++++------ 2 files changed, 59 insertions(+), 12 deletions(-)
Index: linux/arch/x86/lib/delay_32.c =================================================================== --- linux.orig/arch/x86/lib/delay_32.c +++ linux/arch/x86/lib/delay_32.c @@ -38,18 +38,41 @@ static void delay_loop(unsigned long loo :"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, 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(now); - } while ((now-bclock) < loops); - preempt_enable(); + cpu = smp_processor_id(); + preempt_enable(); + + if (prev_cpu != cpu) { + /* + * We have migrated, we skip this small amount of time: + */ + prev = now; + prev_cpu = cpu; + } + } while ((now-prev) < left); } /* Index: linux/arch/x86/lib/delay_64.c =================================================================== --- linux.orig/arch/x86/lib/delay_64.c +++ linux/arch/x86/lib/delay_64.c @@ -26,18 +26,42 @@ int read_current_timer(unsigned long *ti 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, 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(now); + cpu = smp_processor_id(); + preempt_enable(); + + if (prev_cpu != cpu) { + /* + * We have migrated, we skip this small amount of time: + */ + prev = now; + prev_cpu = cpu; + } } - while ((now-bclock) < loops); - preempt_enable(); + while ((now-prev) < left); } EXPORT_SYMBOL(__delay); - 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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