Commit 7eb7ce4d authored by David Vrabel's avatar David Vrabel Committed by Konrad Rzeszutek Wilk
Browse files

xen: correctly check for pending events when restoring irq flags



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)

CC: stable@kernel.org
Acked-by: default avatarIan Campbell <ian.campbell@citrix.com>
Signed-off-by: default avatarDavid Vrabel <david.vrabel@citrix.com>
Signed-off-by: default avatarKonrad Rzeszutek Wilk <konrad.wilk@oracle.com>
parent b930fe5e
......@@ -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)
......
Markdown is supported
0% or .
You are about to add 0 people to the discussion. Proceed with caution.
Finish editing this message first!
Please register or to comment