From mboxrd@z Thu Jan 1 00:00:00 1970 From: Ian Campbell Subject: Re: [PATCH] xen: arm: wait 1000ms for a CPU to come up, instead of forever Date: Wed, 14 Jan 2015 14:39:19 +0000 Message-ID: <1421246359.19103.269.camel@citrix.com> References: <1421244060-1745-1-git-send-email-ian.campbell@citrix.com> <54B67CCA.9060205@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <54B67CCA.9060205@linaro.org> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Julien Grall Cc: stefano.stabellini@eu.citrix.com, tim@xen.org, xen-devel@lists.xen.org List-Id: xen-devel@lists.xenproject.org On Wed, 2015-01-14 at 14:27 +0000, Julien Grall wrote: > Hi Ian, > > On 14/01/15 14:01, Ian Campbell wrote: > > Otherwise continue without it, which is preferable to the current > > infinite hang. > > Nice! > > > Slightly tweak the grammar of a comment in the same function. > > > > Signed-off-by: Ian Campbell > > --- > > xen/arch/arm/smpboot.c | 26 ++++++++++++++++++++++++-- > > 1 file changed, 24 insertions(+), 2 deletions(-) > > > > diff --git a/xen/arch/arm/smpboot.c b/xen/arch/arm/smpboot.c > > index 14054ae..12538d4 100644 > > --- a/xen/arch/arm/smpboot.c > > +++ b/xen/arch/arm/smpboot.c > > @@ -357,6 +357,7 @@ int __init cpu_up_send_sgi(int cpu) > > int __cpu_up(unsigned int cpu) > > { > > int rc; > > + s_time_t deadline; > > > > printk("Bringing up CPU%d\n", cpu); > > > > @@ -369,7 +370,7 @@ int __cpu_up(unsigned int cpu) > > /* Tell the remote CPU which stack to boot on. */ > > init_data.stack = idle_vcpu[cpu]->arch.stack; > > > > - /* Tell the remote CPU what is it's logical CPU ID */ > > + /* Tell the remote CPU what its logical CPU ID is. */ > > init_data.cpuid = cpu; > > > > /* Open the gate for this CPU */ > > @@ -386,12 +387,33 @@ int __cpu_up(unsigned int cpu) > > return rc; > > } > > > > - while ( !cpu_online(cpu) ) > > + deadline = NOW() + MILLISECS(1000); > > Most of cpu_up callbacks are waiting for the CPU to come back. Where do you mean exactly? > I guess > this deadline is for the time to initialize the CPU for Xen? If so, > maybe you can add a comment for it. I would have thought it was evident from the patch that it is how long we will wait for cpu_online(cpu) to become true. Does that really need explaining in prose? > Also, any reason for 1s? Anything taking longer than that is pretty broken IMHO. It also happens to be the Linux time out. > > > + > > + while ( !cpu_online(cpu) && NOW() < deadline ) > > { > > cpu_relax(); > > process_pending_softirqs(); > > } > > > > + /* > > + * Nuke start of day info before checking one last time if the CPU > > + * actually came online. > > + * > > + * Doesn't completely avoid the posibility of it trying to > > + * progress with another CPUs stack etc, but better than nothing, > > + * hopefully. > > + */ > > + init_data.stack = NULL; > > + init_data.cpuid = ~0; > > + smp_up_cpu = MPIDR_INVALID; > > + clean_dcache(smp_up_cpu); > > I don't understand why you need to do this. Is it for pure clean up? If > so, please explain it in the commit message. Is the comment right above it not sufficient explanation? I can insert at the end of the first paragraph "If it is not online it may still be trying and may show up later" is that would help. Ian.