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

[Pavan Nikhilesh Bhagavatula <pbhagavatula@marvell.com>]

Hi Gavin,

>Hi Pavan,
>
>> -----Original Message-----
>> From: pbhagavatula@marvell.com <pbhagavatula@marvell.com>
>> Sent: Friday, February 14, 2020 2:45 PM
>> To: jerinj@marvell.com; Pavan Nikhilesh
><pbhagavatula@marvell.com>
>> Cc: Gavin Hu <Gavin.Hu@arm.com>; dev@dpdk.org
>> Subject: [dpdk-dev] [PATCH] event/octeontx2: remove WFE from
>dualslot
>> dequeue
>>
>> From: Pavan Nikhilesh <pbhagavatula@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.
>
>Does SSO still signal EVENTI to exit from WFE?  Then the core ignore it?

All transactions on SSO bus take the core out of WFE.

>Can this be disabled as WFE is removed?

This can't be disabled.

>
>>
>> Signed-off-by: Pavan Nikhilesh <pbhagavatula@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,jit
>ter=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,jit
>ter=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