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Tue, 10 Oct 2023 23:05:36 -0400 X-MC-Unique: ss5hYIS7PfysupHzS3n9rA-1 Received: from smtp.corp.redhat.com (int-mx10.intmail.prod.int.rdu2.redhat.com [10.11.54.10]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id B969C3C0DF84; Wed, 11 Oct 2023 03:05:35 +0000 (UTC) Received: from piliu.users.ipa.redhat.com (unknown [10.72.120.9]) by smtp.corp.redhat.com (Postfix) with ESMTPS id CF8A6492C3E; Wed, 11 Oct 2023 03:05:31 +0000 (UTC) Date: Wed, 11 Oct 2023 11:05:26 +0800 From: Pingfan Liu To: Hari Bathini Subject: Re: [PATCHv8 3/5] powerpc/setup: Handle the case when boot_cpuid greater than nr_cpus Message-ID: References: <20231009113036.45988-1-piliu@redhat.com> <20231009113036.45988-4-piliu@redhat.com> <8216e3e3-8475-158f-dc79-1b5ba1032150@linux.ibm.com> MIME-Version: 1.0 In-Reply-To: <8216e3e3-8475-158f-dc79-1b5ba1032150@linux.ibm.com> X-Scanned-By: MIMEDefang 3.1 on 10.11.54.10 X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Type: text/plain; charset=us-ascii Content-Disposition: inline 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: , Cc: Baoquan He , kexec@lists.infradead.org, Mahesh Salgaonkar , Nicholas Piggin , Ming Lei , Wen Xiong , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Tue, Oct 10, 2023 at 01:56:13PM +0530, Hari Bathini wrote: > > > On 09/10/23 5:00 pm, Pingfan Liu wrote: > > If the boot_cpuid is smaller than nr_cpus, it requires extra effort to > > ensure the boot_cpu is in cpu_present_mask. This can be achieved by > > reserving the last quota for the boot cpu. > > > > Note: the restriction on nr_cpus will be lifted with more effort in the > > successive patches > > > > Signed-off-by: Pingfan Liu > > Cc: Michael Ellerman > > Cc: Nicholas Piggin > > Cc: Christophe Leroy > > Cc: Mahesh Salgaonkar > > Cc: Wen Xiong > > Cc: Baoquan He > > Cc: Ming Lei > > Cc: kexec@lists.infradead.org > > To: linuxppc-dev@lists.ozlabs.org > > --- > > arch/powerpc/kernel/setup-common.c | 25 ++++++++++++++++++++++--- > > 1 file changed, 22 insertions(+), 3 deletions(-) > > > > diff --git a/arch/powerpc/kernel/setup-common.c b/arch/powerpc/kernel/setup-common.c > > index 81291e13dec0..f9ef0a2666b0 100644 > > --- a/arch/powerpc/kernel/setup-common.c > > +++ b/arch/powerpc/kernel/setup-common.c > > @@ -454,8 +454,8 @@ struct interrupt_server_node { > > void __init smp_setup_cpu_maps(void) > > { > > struct device_node *dn; > > - int shift = 0, cpu = 0; > > - int j, nthreads = 1; > > + int terminate, shift = 0, cpu = 0; > > + int j, bt_thread = 0, nthreads = 1; > > int len; > > struct interrupt_server_node *intserv_node, *n; > > struct list_head *bt_node, head; > > @@ -518,6 +518,7 @@ void __init smp_setup_cpu_maps(void) > > for (j = 0 ; j < nthreads; j++) { > > if (be32_to_cpu(intserv[j]) == boot_cpu_hwid) { > > bt_node = &intserv_node->node; > > + bt_thread = j; > > found_boot_cpu = true; > > /* > > * Record the round-shift between dt > > @@ -537,11 +538,21 @@ void __init smp_setup_cpu_maps(void) > > /* Select the primary thread, the boot cpu's slibing, as the logic 0 */ > > list_add_tail(&head, bt_node); > > pr_info("the round shift between dt seq and the cpu logic number: %d\n", shift); > > + terminate = nr_cpu_ids; > > list_for_each_entry(intserv_node, &head, node) { > > + j = 0; > > > + /* Choose a start point to cover the boot cpu */ > > + if (nr_cpu_ids - 1 < bt_thread) { > > + /* > > + * The processor core puts assumption on the thread id, > > + * not to breach the assumption. > > + */ > > + terminate = nr_cpu_ids - 1; > > nthreads is anyway assumed to be same for all cores. So, enforcing > nr_cpu_ids to a minimum of nthreads (and multiple of nthreads) should > make the code much simpler without the need for above check and the > other complexities addressed in the subsequent patches... > Indeed, this series can be splited into two partsk, [1-2/5] and [3-5/5]. In [1-2/5], if smaller, the nr_cpu_ids is enforced to be equal to nthreads. I will make it align upward on nthreads in the next version. So [1-2/5] can be totally independent from the rest patches in this series. >From an engineer's perspective, [3-5/5] are added to maintain the nr_cpus semantics. (Finally, nr_cpus=1 can be achieved but requiring effort on other subsystem) Testing result on my Power9 machine with SMT=4 -1. taskset -c 4 bash -c 'echo c > /proc/sysrq-trigger' kdump:/# cat /proc/meminfo | grep Percpu Percpu: 896 kB kdump:/# cat /sys/devices/system/cpu/possible 0 -2. taskset -c 5 bash -c 'echo c > /proc/sysrq-trigger' kdump:/# cat /proc/meminfo | grep Percpu Percpu: 1792 kB kdump:/# cat /sys/devices/system/cpu/possible 0-1 -3. taskset -c 6 bash -c 'echo c > /proc/sysrq-trigger' kdump:/# cat /proc/meminfo | grep Percpu Percpu: 1792 kB kdump:/# cat /sys/devices/system/cpu/possible 0,2 -4. taskset -c 7 bash -c 'echo c > /proc/sysrq-trigger' kdump:/# cat /proc/meminfo | grep Percpu Percpu: 1792 kB kdump:/# cat /sys/devices/system/cpu/possible 0,3 Thanks, Pingfan