Messages in this thread Patch in this message | | | Date | Fri, 24 Oct 2014 10:54:37 +0200 | From | Peter Zijlstra <> | Subject | Re: [PATCH v12 09/11] pvqspinlock, x86: Add para-virtualization support |
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On Thu, Oct 16, 2014 at 02:10:38PM -0400, Waiman Long wrote:
> Since enabling paravirt spinlock will disable unlock function inlining, > a jump label can be added to the unlock function without adding patch > sites all over the kernel.
But you don't have to. My patches allowed for the inline to remain, again reducing the overhead of enabling PV spinlocks while running on a real machine.
Look at:
http://lkml.kernel.org/r/20140615130154.213923590@chello.nl
In particular this hunk:
Index: linux-2.6/arch/x86/kernel/paravirt_patch_64.c =================================================================== --- linux-2.6.orig/arch/x86/kernel/paravirt_patch_64.c +++ linux-2.6/arch/x86/kernel/paravirt_patch_64.c @@ -22,6 +22,10 @@ DEF_NATIVE(pv_cpu_ops, swapgs, "swapgs") DEF_NATIVE(, mov32, "mov %edi, %eax"); DEF_NATIVE(, mov64, "mov %rdi, %rax");
+#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUE_SPINLOCK) +DEF_NATIVE(pv_lock_ops, queue_unlock, "movb $0, (%rdi)"); +#endif + unsigned paravirt_patch_ident_32(void *insnbuf, unsigned len) { return paravirt_patch_insns(insnbuf, len, @@ -61,6 +65,9 @@ unsigned native_patch(u8 type, u16 clobb PATCH_SITE(pv_cpu_ops, clts); PATCH_SITE(pv_mmu_ops, flush_tlb_single); PATCH_SITE(pv_cpu_ops, wbinvd); +#if defined(CONFIG_PARAVIRT_SPINLOCKS) && defined(CONFIG_QUEUE_SPINLOCK) + PATCH_SITE(pv_lock_ops, queue_unlock); +#endif
patch_site: ret = paravirt_patch_insns(ibuf, len, start, end);
That makes sure to overwrite the callee-saved call to the pv_lock_ops::queue_unlock with the immediate asm "movb $0, (%rdi)".
Therefore you can retain the inlined unlock with hardly (there might be some NOP padding) any overhead at all. On PV it reverts to a callee saved function call.
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