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Mon, 20 Jul 2020 08:58:16 +0000 (GMT) Received: from b01ledav003.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 130E4B205F; Mon, 20 Jul 2020 08:58:16 +0000 (GMT) Received: from sofia.ibm.com (unknown [9.85.72.83]) by b01ledav003.gho.pok.ibm.com (Postfix) with ESMTP; Mon, 20 Jul 2020 08:58:16 +0000 (GMT) Received: by sofia.ibm.com (Postfix, from userid 1000) id 893012E48B1; Mon, 20 Jul 2020 14:28:12 +0530 (IST) Date: Mon, 20 Jul 2020 14:28:12 +0530 From: Gautham R Shenoy To: Srikar Dronamraju Subject: Re: [PATCH 05/11] powerpc/smp: Dont assume l2-cache to be superset of sibling Message-ID: <20200720085812.GA6680@in.ibm.com> References: <20200714043624.5648-1-srikar@linux.vnet.ibm.com> <20200714043624.5648-6-srikar@linux.vnet.ibm.com> <20200717060011.GE25851@in.ibm.com> <20200720064504.GD21103@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20200720064504.GD21103@linux.vnet.ibm.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.235, 18.0.687 definitions=2020-07-20_04:2020-07-17, 2020-07-20 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 malwarescore=0 spamscore=0 lowpriorityscore=0 clxscore=1015 mlxscore=0 bulkscore=0 adultscore=0 phishscore=0 priorityscore=1501 suspectscore=0 mlxlogscore=999 impostorscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2006250000 definitions=main-2007200065 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: ego@linux.vnet.ibm.com Cc: Nathan Lynch , Gautham R Shenoy , Oliver OHalloran , Michael Neuling , Michael Ellerman , Anton Blanchard , linuxppc-dev , Nick Piggin Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" Hi Srikar, On Mon, Jul 20, 2020 at 12:15:04PM +0530, Srikar Dronamraju wrote: > * Gautham R Shenoy [2020-07-17 11:30:11]: > > > Hi Srikar, > > > > On Tue, Jul 14, 2020 at 10:06:18AM +0530, Srikar Dronamraju wrote: > > > Current code assumes that cpumask of cpus sharing a l2-cache mask will > > > always be a superset of cpu_sibling_mask. > > > > > > Lets stop that assumption. > > > > > > Cc: linuxppc-dev > > > Cc: Michael Ellerman > > > Cc: Nick Piggin > > > Cc: Oliver OHalloran > > > Cc: Nathan Lynch > > > Cc: Michael Neuling > > > Cc: Anton Blanchard > > > Cc: Gautham R Shenoy > > > Cc: Vaidyanathan Srinivasan > > > Signed-off-by: Srikar Dronamraju > > > --- > > > arch/powerpc/kernel/smp.c | 28 +++++++++++++++------------- > > > 1 file changed, 15 insertions(+), 13 deletions(-) > > > > > > diff --git a/arch/powerpc/kernel/smp.c b/arch/powerpc/kernel/smp.c > > > index 7d430fc536cc..875f57e41355 100644 > > > --- a/arch/powerpc/kernel/smp.c > > > +++ b/arch/powerpc/kernel/smp.c > > > @@ -1198,6 +1198,7 @@ static bool update_mask_by_l2(int cpu, struct cpumask *(*mask_fn)(int)) > > > struct device_node *l2_cache, *np; > > > int i; > > > > > > + cpumask_set_cpu(cpu, mask_fn(cpu)); > > > > It would be good to comment why do we need to do set the CPU in the > > l2-mask if we don't have a l2cache domain. > > > > Good Catch, > We should move this after the cpu_to_l2cache. > > > > l2_cache = cpu_to_l2cache(cpu); > > > if (!l2_cache) > > > return false; > > > @@ -1284,29 +1285,30 @@ static void add_cpu_to_masks(int cpu) > > > * add it to it's own thread sibling mask. > > > */ > > > cpumask_set_cpu(cpu, cpu_sibling_mask(cpu)); > > > + cpumask_set_cpu(cpu, cpu_core_mask(cpu)); > > > > > > for (i = first_thread; i < first_thread + threads_per_core; i++) > > > if (cpu_online(i)) > > > set_cpus_related(i, cpu, cpu_sibling_mask); > > > > > > add_cpu_to_smallcore_masks(cpu); > > > - /* > > > - * Copy the thread sibling mask into the cache sibling mask > > > - * and mark any CPUs that share an L2 with this CPU. > > > - */ > > > - for_each_cpu(i, cpu_sibling_mask(cpu)) > > > - set_cpus_related(cpu, i, cpu_l2_cache_mask); > > > update_mask_by_l2(cpu, cpu_l2_cache_mask); > > > > > > - /* > > > - * Copy the cache sibling mask into core sibling mask and mark > > > - * any CPUs on the same chip as this CPU. > > > - */ > > > - for_each_cpu(i, cpu_l2_cache_mask(cpu)) > > > - set_cpus_related(cpu, i, cpu_core_mask); > > > + if (pkg_id == -1) { > > > + struct cpumask *(*mask)(int) = cpu_sibling_mask; > > > + > > > + /* > > > + * Copy the sibling mask into core sibling mask and > > > + * mark any CPUs on the same chip as this CPU. > > > + */ > > > + if (shared_caches) > > > + mask = cpu_l2_cache_mask; > > > + > > > > > > Now that we decoupling the containment relationship between > > sibling_mask and l2-cache mask, should we set all the CPUs that are > > both in cpu_sibling_mask(cpu) as well as cpu_l2_mask(cpu) in > > cpu_core_mask ? > > > > Are you saying instead of setting this cpu in this cpu_core_mask, can we set > all the cpus in the mask in cpu_core_mask? No. What I am referring to is in the for-loop below, you are setting the CPUs that are set in mask(cpu) in the cpu_core_mask. Now, the above code sets mask(cpu) == cpu_sibling_mask(cpu) in the absence of shared_caches, and == cpu_l2_cache_mask(cpu) in the presence of shared_cache. Since we have decoupled the assumption that cpu_sibling_mask(cpu) may not be contained within cpu_l2_cache_mask(cpu), in the presence of a shared-cache, why are we only picking the CPUs in cpu_l2_cache_mask(cpu) to be set in cpu_core_maks(cpu) ? It should ideally be the superset whose CPUs should be set in cpu_core_mask(cpu). And the correct cpuset is cpumask_or(cpu_sibling_mask(cpu), cpu_l2_cache_mask(cpu)) > Currently we dont know if any of the cpus of the mask were already set or > not. Plus we need to anyway update cpumask of all other cpus to says they > are related. So setting a mask instead of cpu at a time will not change > anything for our side. > > > > + for_each_cpu(i, mask(cpu)) > > > + set_cpus_related(cpu, i, cpu_core_mask); > > > > > > - if (pkg_id == -1) > > > return; > > > + } > > > > > > for_each_cpu(i, cpu_online_mask) > > > if (get_physical_package_id(i) == pkg_id) > > > -- > > > 2.17.1 > > > > > -- > > Thanks and Regards > > gautham. > > -- > Thanks and Regards > Srikar Dronamraju