From 585bfaac76e8392e83e82b7457de2f326f29fded Mon Sep 17 00:00:00 2001 From: David Vrabel Date: Thu, 26 Apr 2012 19:44:06 +0100 Subject: [PATCH 1/1] xen: correctly check for pending events when restoring irq flags commit 7eb7ce4d2e8991aff4ecb71a81949a907ca755ac upstream. In xen_restore_fl_direct(), xen_force_evtchn_callback() was being called even if no events were pending. This resulted in (depending on workload) about a 100 times as many xen_version hypercalls as necessary. Fix this by correcting the sense of the conditional jump. This seems to give a significant performance benefit for some workloads. There is some subtle tricksy "..since the check here is trying to check both pending and masked in a single cmpw, but I think this is correct. It will call check_events now only when the combined mask+pending word is 0x0001 (aka unmasked, pending)." (Ian) Acked-by: Ian Campbell Signed-off-by: David Vrabel Signed-off-by: Konrad Rzeszutek Wilk Signed-off-by: Ben Hutchings --- arch/x86/xen/xen-asm.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/xen/xen-asm.S b/arch/x86/xen/xen-asm.S index 79d7362ad6d1..3e45aa000718 100644 --- a/arch/x86/xen/xen-asm.S +++ b/arch/x86/xen/xen-asm.S @@ -96,7 +96,7 @@ ENTRY(xen_restore_fl_direct) /* check for unmasked and pending */ cmpw $0x0001, PER_CPU_VAR(xen_vcpu_info) + XEN_vcpu_info_pending - jz 1f + jnz 1f 2: call check_events 1: ENDPATCH(xen_restore_fl_direct) -- 2.39.2