From mboxrd@z Thu Jan 1 00:00:00 1970 From: Peter Zijlstra Subject: Re: linux-next: build failure after merge of the tip tree Date: Tue, 14 Jan 2014 21:05:47 +0100 Message-ID: <20140114200547.GM7572@laptop.programming.kicks-ass.net> References: <20140114142627.537a702607e703c6eff63640@canb.auug.org.au> <20140114141406.GD7572@laptop.programming.kicks-ass.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-kernel-owner@vger.kernel.org To: Mikulas Patocka Cc: Stephen Rothwell , Thomas Gleixner , Ingo Molnar , "H. Peter Anvin" , "Rafael J. Wysocki" , linux-next@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-next.vger.kernel.org Archived-At: List-Archive: List-Post: On Tue, Jan 14, 2014 at 02:06:57PM -0500, Mikulas Patocka wrote: > On Tue, 14 Jan 2014, Peter Zijlstra wrote: > > > Caused by commit 62b94a08da1b ("sched/preempt: Take away > > > preempt_enable_no_resched() from modules") Read these two lines, then note that: > Try adding #include to speedstep-lib.c. Does it help? this obviously will not work as preempt_check_resched() and preempt_enable_no_resched() are no longer available to modules. > > I think that pm commit is a very good example of why the sched/preempt > > patch is a very good idea. > > > > Also that Changelog fails to explain why enabling interrupts helps. What > > interrupt is required for progress, and how does it make the progress > > happen. > > There is no explanation. It's hardware issue and I have no documentation > for the hardware. Rafael works for Intel, he ought to be able to figure out wtf the hardware does/needs. > The general problem is that if there are bus-master transfers running (or > possibly for other hardware reasons), the CPU refuses to change frequency. > You can wait a little bit and retry and maybe you succeed changing the > frequency next time. > > If you enable interrupts, wait, disable interrupts and retry, you may > succeed. If you keep interrupts disabled and retry, you never succeed, no > matter how long do you wait. I found it experimentally, I don't know > reason for that. Sounds like magic goo.. In any case, try the below, it does the same but is far less horrid. --- drivers/cpufreq/speedstep-smi.c | 4 ++++ 1 file changed, 4 insertions(+) diff --git a/drivers/cpufreq/speedstep-smi.c b/drivers/cpufreq/speedstep-smi.c index 0f5326d6f79f..57d31538c248 100644 --- a/drivers/cpufreq/speedstep-smi.c +++ b/drivers/cpufreq/speedstep-smi.c @@ -188,6 +188,7 @@ static void speedstep_set_state(unsigned int state) return; /* Disable IRQs */ + preempt_disable(); local_irq_save(flags); command = (smi_sig & 0xffffff00) | (smi_cmd & 0xff); @@ -200,7 +201,9 @@ static void speedstep_set_state(unsigned int state) if (retry) { pr_debug("retry %u, previous result %u, waiting...\n", retry, result); + local_irq_restore(flags); mdelay(retry * 50); + local_irq_save(flags); } retry++; __asm__ __volatile__( @@ -217,6 +220,7 @@ static void speedstep_set_state(unsigned int state) /* enable IRQs */ local_irq_restore(flags); + preempt_enable(); if (new_state == state) pr_debug("change to %u MHz succeeded after %u tries "