netdev - Re: [PATCH] Fix build errors on 32bit platforms with new ktime

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Message-ID: <20070424145754.1a37f666@dxpl.pdx.osdl.net>
Date:	Tue, 24 Apr 2007 14:57:54 -0700
From:	Stephen Hemminger <shemminger@...ux-foundation.org>
To:	YOSHIFUJI Hideaki / 吉藤英明 
	<yoshfuji@...ux-ipv6.org>
Cc:	dada1@...mosbay.com, bunk@...sta.de, davem@...emloft.net,
	netdev@...r.kernel.org, tglx@...utronix.de, yoshfuji@...ux-ipv6.org
Subject: Re: [PATCH] Fix build errors on 32bit platforms with new ktime

On Wed, 25 Apr 2007 06:55:39 +0900 (JST)
YOSHIFUJI Hideaki / 吉藤英明  <yoshfuji@...ux-ipv6.org> wrote:

> In article <20070424100420.2860db68@...l.pdx.osdl.net> (at Tue, 24 Apr 2007 10:04:20 -0700), Stephen Hemminger <shemminger@...ux-foundation.org> says:
> 
> > Yoshifuji-san had the right idea, but ktime_to_us needs to be defined
> > in a way that works on both 64 and 32bit platforms.
> 
> No, this does not cure.
> >  
> > +#define ktime_to_us(kt)			((kt).tv64 / NSEC_PER_SEC)
> > +
> 
> NSEC_PER_USEC?

On 64 bit platforms, ktime stores nano-seconds in a 64 bit value, so
this is correct.

> 
> > +static inline s64 ktime_to_us(const ktime_t kt)
> > +{
> > +	return (s64) kt.tv_sec * USEC_PER_SEC + kt.tv_nsec / NSEC_PER_USEC;
> > +}
> > +
> 
> Please do NOT use division here, which was the source of the
> linkage error, and the reason why I posted a patch to use
> ktime_to_timeval().

On 32 bit platforms, ktime stores as two 32 bit values. Therefore the
division is only 32bit and therefore okay.

Corrected patch.
---------------------------
>From 04d3583fbb763deeb9d33c90239a8d35e66e0c1e Mon Sep 17 00:00:00 2001
From: Stephen Hemminger <shemminger@...ux-foundation.org>
Date: Tue, 24 Apr 2007 12:44:33 -0700
Subject: [PATCH] ktime_to_us: for TCP usage.

Argh, Monday sucks.  Sorry, need to build on 32bit every time...

Signed-off-by: Stephen Hemminger <shemminger@...ux-foundation.org>
---
 include/linux/ktime.h   |   13 +++++++++++++
 net/ipv4/tcp_illinois.c |    2 +-
 net/ipv4/tcp_lp.c       |    2 +-
 net/ipv4/tcp_vegas.c    |    2 +-
 net/ipv4/tcp_veno.c     |    2 +-
 5 files changed, 17 insertions(+), 4 deletions(-)

diff --git a/include/linux/ktime.h b/include/linux/ktime.h
index 248305b..3793490 100644
--- a/include/linux/ktime.h
+++ b/include/linux/ktime.h
@@ -121,6 +121,8 @@ static inline ktime_t timeval_to_ktime(struct timeval tv)
 /* Convert ktime_t to nanoseconds - NOP in the scalar storage format: */
 #define ktime_to_ns(kt)			((kt).tv64)
 
+#define ktime_to_us(kt)			((kt).tv64 / NSEC_PER_SEC)
+
 #else
 
 /*
@@ -257,6 +259,17 @@ static inline s64 ktime_to_ns(const ktime_t kt)
 	return (s64) kt.tv.sec * NSEC_PER_SEC + kt.tv.nsec;
 }
 
+/**
+ * ktime_to_us - convert a ktime_t variable to scalar microseconds
+ * @kt:		the ktime_t variable to convert
+ *
+ * Returns the scalar nanoseconds representation of @kt
+ */
+static inline s64 ktime_to_us(const ktime_t kt)
+{
+	return (s64) kt.tv.sec * USEC_PER_SEC + kt.tv.nsec / NSEC_PER_USEC;
+}
+
 #endif
 
 /*
diff --git a/net/ipv4/tcp_illinois.c b/net/ipv4/tcp_illinois.c
index 8e31659..4adc47c 100644
--- a/net/ipv4/tcp_illinois.c
+++ b/net/ipv4/tcp_illinois.c
@@ -90,7 +90,7 @@ static void tcp_illinois_acked(struct sock *sk, u32 pkts_acked, ktime_t last)
 
 	ca->acked = pkts_acked;
 
-	rtt = ktime_to_ns(net_timedelta(last)) / NSEC_PER_USEC;
+	rtt = ktime_to_us(net_timedelta(last));
 
 	/* ignore bogus values, this prevents wraparound in alpha math */
 	if (rtt > RTT_MAX)
diff --git a/net/ipv4/tcp_lp.c b/net/ipv4/tcp_lp.c
index b4e062a..43294ad 100644
--- a/net/ipv4/tcp_lp.c
+++ b/net/ipv4/tcp_lp.c
@@ -266,7 +266,7 @@ static void tcp_lp_pkts_acked(struct sock *sk, u32 num_acked, ktime_t last)
 	struct tcp_sock *tp = tcp_sk(sk);
 	struct lp *lp = inet_csk_ca(sk);
 
-	tcp_lp_rtt_sample(sk,  ktime_to_ns(net_timedelta(last)) / NSEC_PER_USEC);
+	tcp_lp_rtt_sample(sk,  ktime_to_us(net_timedelta(last)));
 
 	/* calc inference */
 	if (tcp_time_stamp > tp->rx_opt.rcv_tsecr)
diff --git a/net/ipv4/tcp_vegas.c b/net/ipv4/tcp_vegas.c
index 0f0ee7f..73e19cf 100644
--- a/net/ipv4/tcp_vegas.c
+++ b/net/ipv4/tcp_vegas.c
@@ -118,7 +118,7 @@ void tcp_vegas_pkts_acked(struct sock *sk, u32 cnt, ktime_t last)
 	u32 vrtt;
 
 	/* Never allow zero rtt or baseRTT */
-	vrtt = (ktime_to_ns(net_timedelta(last)) / NSEC_PER_USEC) + 1;
+	vrtt = ktime_to_us(net_timedelta(last)) + 1;
 
 	/* Filter to find propagation delay: */
 	if (vrtt < vegas->baseRTT)
diff --git a/net/ipv4/tcp_veno.c b/net/ipv4/tcp_veno.c
index 0b50d06..9edb340 100644
--- a/net/ipv4/tcp_veno.c
+++ b/net/ipv4/tcp_veno.c
@@ -75,7 +75,7 @@ static void tcp_veno_pkts_acked(struct sock *sk, u32 cnt, ktime_t last)
 	u32 vrtt;
 
 	/* Never allow zero rtt or baseRTT */
-	vrtt = (ktime_to_ns(net_timedelta(last)) / NSEC_PER_USEC) + 1;
+	vrtt = ktime_to_us(net_timedelta(last)) + 1;
 
 	/* Filter to find propagation delay: */
 	if (vrtt < veno->basertt)
-- 
1.5.0.6

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