netdev - Re: [patch] pktgen: bug when calling ndelay in x86 architectures

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Message-ID: <1318949264.2657.97.camel@edumazet-HP-Compaq-6005-Pro-SFF-PC>
Date:	Tue, 18 Oct 2011 16:47:44 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	Daniel Turull <daniel.turull@...il.com>,
	David Miller <davem@...emloft.net>, netdev@...r.kernel.org,
	Robert Olsson <robert@...julf.net>,
	Voravit Tanyingyong <voravit@....se>,
	Jens Laas <jens.laas@...m.uu.se>
Subject: Re: [patch] pktgen: bug when calling ndelay in x86 architectures

Le mardi 18 octobre 2011 à 15:00 +0100, Ben Hutchings a écrit :

> AIUI, the reason for limits on delays is not that it's bad practice to
> spin for so long, but that the delay calculations may overflow or
> otherwise become inaccurate.

OK, I can understand that, then a more appropriate patch would be :


diff --git a/net/core/pktgen.c b/net/core/pktgen.c
index 796044a..28bbf5b 100644
--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -2145,9 +2145,12 @@ static void spin(struct pktgen_dev *pkt_dev, ktime_t spin_until)
 	}
 
 	start_time = ktime_now();
-	if (remaining < 100000)
-		ndelay(remaining);	/* really small just spin */
-	else {
+	if (remaining < 100000) {
+		if (remaining >= 10000)
+			udelay(remaining/1000);
+		else
+			ndelay(remaining);
+	} else {
 		/* see do_nanosleep */
 		hrtimer_init_sleeper(&t, current);
 		do {


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