Re: [PATCH] Reduce TLB flushing during process migration

[Manfred Spraul <manfred@colorfullife.com>]

Martin wrote:

>diff -Nru a/kernel/sched.c b/kernel/sched.c
>--- a/kernel/sched.c	Tue Feb 17 07:33:59 2004
>+++ b/kernel/sched.c	Tue Feb 17 07:33:59 2004
>@@ -25,6 +25,7 @@
> #include <linux/highmem.h>
> #include <linux/smp_lock.h>
> #include <asm/mmu_context.h>
>+#include <asm/tlbflush.h>
> #include <linux/interrupt.h>
> #include <linux/completion.h>
> #include <linux/kernel_stat.h>
>@@ -1135,6 +1136,14 @@
> 		task_rq_unlock(rq, &flags);
> 		wake_up_process(rq->migration_thread);
> 		wait_for_completion(&req.done);
>+
>+		/*
>+		 * we want a new context here. This eliminates TLB
>+		 * flushes on the cpus where the process executed prior to
>+		 * the migration.
>+		 */
>+		flush_tlb_mm(current->mm);
>+
>  
>
I think flush_tlb_mm() is the wrong function - e.g. for i386, it's a 
wasted flush, because i386 disconnects previous cpus from the tlb flush 
automatically.
And it's always the wrong thing if you've migrated one thread of a task 
that runs on multiple cpus. I think you need a new hook.

--
    Manfred