netdev - RE: [PATCH 2/2] net: fec: optimize IRQ handler

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Date:   Thu, 7 Dec 2017 03:02:58 +0000
From:   Andy Duan <fugang.duan@....com>
To:     Lucas Stach <l.stach@...gutronix.de>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>
CC:     "patchwork-lst@...gutronix.de" <patchwork-lst@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>
Subject: RE: [PATCH 2/2] net: fec: optimize IRQ handler

From: Lucas Stach <l.stach@...gutronix.de> Sent: Thursday, December 07, 2017 1:25 AM
>fep->work_rx and fep->work_tx are both non-zero, as long as the NAPI
>softirq hasn't finished its work. So if the current IRQ does not signal any RX or
>TX completion, but some unrelated event, the path to schedule the NAPI
>context is still entered.
>
>The handler works correctly as in this case napi_schedule_prep() will reject
>the scheduling attempt, but the flow can still be optimized by not trying to
>schedule if the IRQ doesn't signal RX or TX completion.
>
>Signed-off-by: Lucas Stach <l.stach@...gutronix.de>
>---
> drivers/net/ethernet/freescale/fec_main.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
>diff --git a/drivers/net/ethernet/freescale/fec_main.c
>b/drivers/net/ethernet/freescale/fec_main.c
>index 0b70c07eb703..2043e140e9bd 100644
>--- a/drivers/net/ethernet/freescale/fec_main.c
>+++ b/drivers/net/ethernet/freescale/fec_main.c
>@@ -1587,14 +1587,14 @@ fec_enet_interrupt(int irq, void *dev_id)
> 	int_events = readl_relaxed(fep->hwp + FEC_IEVENT) &
> 	             readl_relaxed(fep->hwp + FEC_IMASK);
> 	writel(int_events, fep->hwp + FEC_IEVENT);
>-	fec_enet_collect_events(fep, int_events);
>
>-	if ((fep->work_tx || fep->work_rx) && fep->link) {
>+	if ((int_events & (FEC_ENET_RXF | FEC_ENET_TXF)) && fep->link) {
> 		ret = IRQ_HANDLED;
>
> 		if (napi_schedule_prep(&fep->napi)) {
> 			/* Disable the NAPI interrupts */
> 			writel(FEC_NAPI_IMASK, fep->hwp + FEC_IMASK);
>+			fec_enet_collect_events(fep, int_events);
> 			__napi_schedule(&fep->napi);
> 		}
> 	}
>--
>2.11.0

The patch seems fine, and patch#1 is better to cache imask as David's comment.  
Thanks.

Acked-by: Fugang Duan <fugang.duan@....com>