[dpdk-dev] [PATCH] event/octeontx2: remove WFE from dualslot dequeue

[pbhagavatula at marvell.com]

From: Pavan Nikhilesh <pbhagavatula at marvell.com>

Each workslot is always bound to a specific lcore there is no multi-core
contention to cause cache trashing as a result it is safe to remove the
WFE. Also, in dual workslot dequeue work will mostlikely be available on
the pair workslot making WFE impractical.

Signed-off-by: Pavan Nikhilesh <pbhagavatula at marvell.com>
---

Also, this in-turn reduces the branch misses

Before:
	0 arm_spe_0/ts_enable=1,pct_enable=1,pa_enable=1,branch_filter=1,jitter=1,min_latency=0/
	0 dummy:u
	0 llc-miss
	0 tlb-miss
	853 branch-miss
	0 remote-access
	0 l1d-miss

After:
	0 arm_spe_0/ts_enable=1,pct_enable=1,pa_enable=1,branch_filter=1,jitter=1,min_latency=0/
	0 dummy:u
	0 llc-miss
	0 tlb-miss
	250 branch-miss
	0 remote-access
	0 l1d-miss

WFE Data:

0x4C40 - WFI_WFE_WAIT_CYCLES - Number of cycles waiting at a WFI or WFE instruction.

- WFE Cycles before the patch for Dual workslot
#perf stat -C 20 -e r4C40 sleep 1
Performance counter stats for 'CPU(s) 20':

               264      r4C40
       1.002494168 seconds time elapsed

- WFE Cycles for single workslot
#perf stat -C 20 -e r4C40 sleep 1
Performance counter stats for 'CPU(s) 20':

       908,778,351      r4C40
       1.002598253 seconds time elapsed

 drivers/event/octeontx2/otx2_worker_dual.h | 6 +-----
 1 file changed, 1 insertion(+), 5 deletions(-)

diff --git a/drivers/event/octeontx2/otx2_worker_dual.h b/drivers/event/octeontx2/otx2_worker_dual.h
index 5134e3d52..c88420eb4 100644
--- a/drivers/event/octeontx2/otx2_worker_dual.h
+++ b/drivers/event/octeontx2/otx2_worker_dual.h
@@ -29,11 +29,7 @@ otx2_ssogws_dual_get_work(struct otx2_ssogws_state *ws,
 		rte_prefetch_non_temporal(lookup_mem);
 #ifdef RTE_ARCH_ARM64
 	asm volatile(
-			"        ldr %[tag], [%[tag_loc]]    \n"
-			"        ldr %[wqp], [%[wqp_loc]]    \n"
-			"        tbz %[tag], 63, done%=      \n"
-			"        sevl                        \n"
-			"rty%=:  wfe                         \n"
+			"rty%=:	                             \n"
 			"        ldr %[tag], [%[tag_loc]]    \n"
 			"        ldr %[wqp], [%[wqp_loc]]    \n"
 			"        tbnz %[tag], 63, rty%=      \n"
--
2.17.1