From: Bart Van Assche <Bart.VanAssche@sandisk.com>
To: "jthumshirn@suse.de" <jthumshirn@suse.de>
Cc: "jejb@linux.vnet.ibm.com" <jejb@linux.vnet.ibm.com>,
"hch@infradead.org" <hch@infradead.org>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
"hare@suse.de" <hare@suse.de>,
"martin.petersen@oracle.com" <martin.petersen@oracle.com>,
"linux-scsi@vger.kernel.org" <linux-scsi@vger.kernel.org>,
"arnd@arndb.de" <arnd@arndb.de>
Subject: Re: [PATCH] libfc: fix seconds_since_last_reset miscalculation
Date: Tue, 15 Nov 2016 14:50:17 +0000 [thread overview]
Message-ID: <1479221415.3426.3.camel@sandisk.com> (raw)
In-Reply-To: <20161115091840.7cldqui4dpi7nrz5@linux-x5ow.site>
On Tue, 2016-11-15 at 10:18 +0100, Johannes Thumshirn wrote:
> On Tue, Nov 08, 2016 at 03:04:43PM +0000, Bart Van Assche wrote:
> > I think the above code will miscalculate seconds_since_last_reset
> > if
> > 'jiffies' wraps around after an lport has been created and before
> > seconds_since_last_reset is computed. Shouldn't
> > seconds_since_last_reset
> > be computed as follows?
> >
> > fc_stats->seconds_since_last_reset = (jiffies - boot_time) /
> > HZ;
>
> But what happens when jiffies - boot_time becomes negative? Then we
> reintroduce the bug again and have 'fcoeadm -s' show weird values.
Hello Johannes,
If your concern is about 'jiffies' wrapping around on 32-bit systems
then you should use get_jiffies_64(). get_jiffies_64() - boot_time
can't become negative. It namely takes several million years before a
64-bit HZ counter wraps around.
Bart.
next prev parent reply other threads:[~2016-11-15 14:50 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-11-08 8:44 [PATCH] libfc: fix seconds_since_last_reset miscalculation Johannes Thumshirn
2016-11-08 15:04 ` Bart Van Assche
2016-11-15 9:18 ` Johannes Thumshirn
2016-11-15 14:50 ` Bart Van Assche [this message]
2016-11-15 15:05 ` Johannes Thumshirn
2016-11-16 16:58 ` Arnd Bergmann
2016-11-17 8:12 ` Johannes Thumshirn
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