From: Thomas Gleixner <tglx@linutronix.de>
To: Michael Ellerman <mpe@ellerman.id.au>, linux-kernel@vger.kernel.org
Cc: linux-arch@vger.kernel.org, x86@kernel.org,
dave.hansen@linux.intel.com, mingo@redhat.com, bp@alien8.de,
ldufour@linux.ibm.com, linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH 6/9] cpu/SMT: Allow enabling partial SMT states via sysfs
Date: Sat, 10 Jun 2023 22:09:44 +0200 [thread overview]
Message-ID: <87r0qj84fr.ffs@tglx> (raw)
In-Reply-To: <20230524155630.794584-6-mpe@ellerman.id.au>
On Thu, May 25 2023 at 01:56, Michael Ellerman wrote:
> There is a hook which allows arch code to control how many threads per
Can you please write out architecture in changelogs and comments?
I know 'arch' is commonly used but while my brain parser tolerates
'arch_' prefixes it raises an exception on 'arch' in prose as 'arch' is
a regular word with a completely different meaning. Changelogs and
comments are not space constraint.
> @@ -2505,20 +2505,38 @@ __store_smt_control(struct device *dev, struct device_attribute *attr,
> if (cpu_smt_control == CPU_SMT_NOT_SUPPORTED)
> return -ENODEV;
>
> - if (sysfs_streq(buf, "on"))
> + if (sysfs_streq(buf, "on")) {
> ctrlval = CPU_SMT_ENABLED;
> - else if (sysfs_streq(buf, "off"))
> + num_threads = cpu_smt_max_threads;
> + } else if (sysfs_streq(buf, "off")) {
> ctrlval = CPU_SMT_DISABLED;
> - else if (sysfs_streq(buf, "forceoff"))
> + num_threads = 1;
> + } else if (sysfs_streq(buf, "forceoff")) {
> ctrlval = CPU_SMT_FORCE_DISABLED;
> - else
> + num_threads = 1;
> + } else if (kstrtoint(buf, 10, &num_threads) == 0) {
> + if (num_threads == 1)
> + ctrlval = CPU_SMT_DISABLED;
> + else if (num_threads > 1 && topology_smt_threads_supported(num_threads))
> + ctrlval = CPU_SMT_ENABLED;
> + else
> + return -EINVAL;
> + } else {
> return -EINVAL;
> + }
>
> ret = lock_device_hotplug_sysfs();
> if (ret)
> return ret;
>
> - if (ctrlval != cpu_smt_control) {
> + orig_threads = cpu_smt_num_threads;
> + cpu_smt_num_threads = num_threads;
> +
> + if (num_threads > orig_threads) {
> + ret = cpuhp_smt_enable();
> + } else if (num_threads < orig_threads) {
> + ret = cpuhp_smt_disable(ctrlval);
> + } else if (ctrlval != cpu_smt_control) {
> switch (ctrlval) {
> case CPU_SMT_ENABLED:
> ret = cpuhp_smt_enable();
This switch case does not make sense anymore.
The only situation which reaches this is when the control value goes
from CPU_SMT_DISABLED to CPU_SMT_FORCE_DISABLED because that's not
changing the number of threads.
So something like this is completely sufficient:
if (num_threads > orig_threads)
ret = cpuhp_smt_enable();
else if (num_threads < orig_threads || ctrval == CPU_SMT_FORCE_DISABLED)
ret = cpuhp_smt_disable(ctrlval);
No?
Thanks,
tglx
next prev parent reply other threads:[~2023-06-10 20:18 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-05-24 15:56 [PATCH 1/9] cpu/SMT: Move SMT prototypes into cpu_smt.h Michael Ellerman
2023-05-24 15:56 ` [PATCH 2/9] cpu/SMT: Move smt/control simple exit cases earlier Michael Ellerman
2023-05-24 15:56 ` [PATCH 3/9] cpu/SMT: Store the current/max number of threads Michael Ellerman
2023-06-10 21:26 ` Thomas Gleixner
2023-06-10 22:08 ` Thomas Gleixner
2023-06-13 17:16 ` Laurent Dufour
2023-06-13 18:53 ` Thomas Gleixner
2023-06-14 12:27 ` Laurent Dufour
2023-05-24 15:56 ` [PATCH 4/9] cpu/SMT: Create topology_smt_threads_supported() Michael Ellerman
2023-06-10 22:15 ` Thomas Gleixner
2023-05-24 15:56 ` [PATCH 5/9] cpu/SMT: Create topology_smt_thread_allowed() Michael Ellerman
2023-06-10 22:35 ` Thomas Gleixner
2023-05-24 15:56 ` [PATCH 6/9] cpu/SMT: Allow enabling partial SMT states via sysfs Michael Ellerman
2023-06-10 20:09 ` Thomas Gleixner [this message]
2023-06-10 20:13 ` Thomas Gleixner
2023-05-24 15:56 ` [PATCH 7/9] powerpc/pseries: Initialise CPU hotplug callbacks earlier Michael Ellerman
2023-05-24 15:56 ` [PATCH 8/9] powerpc: Add HOTPLUG_SMT support Michael Ellerman
2023-06-01 13:27 ` Laurent Dufour
2023-06-01 16:19 ` Laurent Dufour
2023-06-10 21:10 ` Thomas Gleixner
2023-06-12 15:20 ` Laurent Dufour
2023-06-12 16:34 ` Thomas Gleixner
2023-05-24 15:56 ` [PATCH 9/9] powerpc/pseries: Honour current SMT state when DLPAR onlining CPUs Michael Ellerman
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