From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: [PATCH RFC] pm_qos_requirement might sleep Date: Thu, 14 Aug 2008 19:48:57 +0200 Message-ID: <1218736137.10800.234.camel@twins> References: <520f0cf10808041352h78bd4319x1802f018aeffe6dc@mail.gmail.com> <1217921101.3589.98.camel@twins> <20080805204901.GA31132@linux.intel.com> <1217970588.29415.36.camel@lappy.programming.kicks-ass.net> <520f0cf10808051518h1459d353r8de78e98f79ec57c@mail.gmail.com> <20080812224926.GA20652@linux.intel.com> <520f0cf10808130124o301b6691ra37ac9007120b9df@mail.gmail.com> <20080814155241.GA31050@linux.intel.com> Mime-Version: 1.0 Content-Type: text/plain Content-Transfer-Encoding: 7bit Cc: John Kacur , LKML , rt-users , Steven Rostedt , Ingo Molnar , Thomas Gleixner , arjan To: mgross@linux.intel.com Return-path: Received: from bombadil.infradead.org ([18.85.46.34]:59202 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751802AbYHNRsz (ORCPT ); Thu, 14 Aug 2008 13:48:55 -0400 In-Reply-To: <20080814155241.GA31050@linux.intel.com> Sender: linux-rt-users-owner@vger.kernel.org List-ID: On Thu, 2008-08-14 at 08:52 -0700, mark gross wrote: > Keeping a lock around the different "target_value"s may not be so > important. Its just a 32bit scaler value, and perhaps we can make it an > atomic type? That way we loose the raw_spinlock. My suggestion was to keep the locking for the write side - so as to avoid stuff stomping on one another, but drop the read side as: spin_lock foo = var; spin_unlock return foo; is kinda useless, it doesn't actually serialize against the usage of foo, that is, once it gets used, var might already have acquired a new value. The only thing it would protect is reading var, but since that is a machine sized read, its atomic anyway (assuming its naturally aligned). So no need for atomic_t (its read-side is just a read too), just drop the whole lock usage from pq_qos_requirement().