[dpdk-dev] [PATCH] event/octeontx2: use wfe while waiting for head
Gavin Hu (Arm Technology China)
Gavin.Hu at arm.com
Thu Oct 24 17:53:21 CEST 2019
Hi Pavan,
> -----Original Message-----
> From: pbhagavatula at marvell.com <pbhagavatula at marvell.com>
> Sent: Thursday, October 24, 2019 12:13 AM
> To: Gavin Hu (Arm Technology China) <Gavin.Hu at arm.com>;
> jerinj at marvell.com; Pavan Nikhilesh <pbhagavatula at marvell.com>
> Cc: dev at dpdk.org
> Subject: [dpdk-dev] [PATCH] event/octeontx2: use wfe while waiting for
> head
>
> From: Pavan Nikhilesh <pbhagavatula at marvell.com>
>
> Use wfe to save power while waiting for tag to become head.
>
> SSO signals EVENTI to allow cores to exit from wfe when they
> are waiting for specific operations in which one of them is
> setting HEAD bit in GWS_TAG.
>
> Signed-off-by: Pavan Nikhilesh <pbhagavatula at marvell.com>
> ---
> drivers/event/octeontx2/otx2_worker.h | 30 ++++++++++++++++++++++++--
> -
> 1 file changed, 27 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/event/octeontx2/otx2_worker.h
> b/drivers/event/octeontx2/otx2_worker.h
> index 4e971f27c..7a55caca5 100644
> --- a/drivers/event/octeontx2/otx2_worker.h
> +++ b/drivers/event/octeontx2/otx2_worker.h
> @@ -226,10 +226,34 @@ otx2_ssogws_swtag_wait(struct otx2_ssogws *ws)
> }
>
> static __rte_always_inline void
> -otx2_ssogws_head_wait(struct otx2_ssogws *ws, const uint8_t wait_flag)
> +otx2_ssogws_head_wait(struct otx2_ssogws *ws)
> {
> - while (wait_flag && !(otx2_read64(ws->tag_op) & BIT_ULL(35)))
> +#ifdef RTE_ARCH_ARM64
> + uint64_t tag;
> +
> + asm volatile (
> + " ldr %[tag], [%[tag_op]] \n"
"ldxr" should be used, exclusive-load is required to "monitor" the location, then a write to the location will cause clear of the exclusive monitor, thus a wake up event is generated implicitly.
You can find more explanation is here:
http://inbox.dpdk.org/dev/AM0PR08MB5363F9D1BA158B66B803EA068F6B0@AM0PR08MB5363.eurprd08.prod.outlook.com/
/Gavin
> + " tbnz %[tag], 35, done%= \n"
> + " sevl \n"
> + "rty%=: wfe \n"
> + " ldr %[tag], [%[tag_op]] \n"
> + " tbz %[tag], 35, rty%= \n"
> + "done%=: \n"
> + : [tag] "=&r" (tag)
> + : [tag_op] "r" (ws->tag_op)
> + );
> +#else
> + /* Wait for the HEAD to be set */
> + while (!(otx2_read64(ws->tag_op) & BIT_ULL(35)))
> ;
> +#endif
> +}
> +
> +static __rte_always_inline void
> +otx2_ssogws_order(struct otx2_ssogws *ws, const uint8_t wait_flag)
> +{
> + if (wait_flag)
> + otx2_ssogws_head_wait(ws);
>
> rte_cio_wmb();
What ordering does this barrier try to keep? If there is a write then wait for kind of response, should this barrier move before otx2_ssogws_head_wait?
/Gavin
> }
> @@ -258,7 +282,7 @@ otx2_ssogws_event_tx(struct otx2_ssogws *ws,
> struct rte_event ev[],
>
> /* Perform header writes before barrier for TSO */
> otx2_nix_xmit_prepare_tso(m, flags);
> - otx2_ssogws_head_wait(ws, !ev->sched_type);
> + otx2_ssogws_order(ws, !ev->sched_type);
> otx2_ssogws_prepare_pkt(txq, m, cmd, flags);
>
> if (flags & NIX_TX_MULTI_SEG_F) {
> --
> 2.17.1
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