From: Matthew Wilcox <willy@linux.intel.com>
To: chetan loke <loke.chetan@gmail.com>
Cc: Tim Chen <tim.c.chen@linux.intel.com>,
linux-fsdevel <linux-fsdevel@vger.kernel.org>,
linux-scsi@vger.kernel.org,
linux-kernel <linux-kernel@vger.kernel.org>,
Andi Kleen <ak@linux.intel.com>
Subject: Re: SCSI RAM driver ported to 3.3 kernel for file system and I/O testing
Date: Wed, 16 May 2012 15:43:32 -0400 [thread overview]
Message-ID: <20120516194332.GN22985@linux.intel.com> (raw)
In-Reply-To: <CAAsGZS5wivyHUGNtHuTNCQQnnqZ=qt-7uSZjbE-7_KC+L-Yoaw@mail.gmail.com>
On Wed, May 16, 2012 at 03:37:56PM -0400, chetan loke wrote:
> On Wed, May 16, 2012 at 3:35 PM, Matthew Wilcox <willy@linux.intel.com> wrote:
> > On Wed, May 16, 2012 at 03:31:55PM -0400, chetan loke wrote:
> >> > + if (list_empty(&ram_device->commands))
> >> > + wake_up_process(ram_device->thread);
> >>
> >> Didn't look in detail but if the queue is empty then why would you
> >> want to wake up the kthread? What if you just wake_up after
> >> list_add_tail below?
> >
> > If the list is non-empty, then the kthread has already been woken up
> > and doesn't need to be woken again.
>
> Sorry, not able to follow. wait_even_interruptible will put kthread to
> sleep. So how will it be already awake?
Consider the following:
CPU 0 CPU 1
->queuecommand
lock
wakes kthread
queues command 1
unlock
->queuecommand
lock
kthread wakes
lock
queues command 2
unlock
dequeues command 1
dequeues command 2
unlock
See? No need to wake the kthread *if there's already something on the
queue*, because you know it was already woken by whoever put the first
command on the queue.
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next prev parent reply other threads:[~2012-05-16 19:42 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-05-16 17:07 SCSI RAM driver ported to 3.3 kernel for file system and I/O testing Tim Chen
2012-05-16 17:18 ` Joe Perches
2012-05-16 19:02 ` Tim Chen
2012-05-16 17:41 ` Bart Van Assche
2012-05-16 19:31 ` chetan loke
2012-05-16 19:35 ` Matthew Wilcox
2012-05-16 19:37 ` chetan loke
2012-05-16 19:43 ` Matthew Wilcox [this message]
2012-05-16 19:54 ` chetan loke
2012-05-16 20:22 ` Matthew Wilcox
2012-05-16 20:05 ` Tim Chen
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