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 3/9] cpu/SMT: Store the current/max number of threads
Date: Sat, 10 Jun 2023 23:26:18 +0200 [thread overview]
Message-ID: <87fs6z80w5.ffs@tglx> (raw)
In-Reply-To: <20230524155630.794584-3-mpe@ellerman.id.au>
On Thu, May 25 2023 at 01:56, Michael Ellerman wrote:
> #ifdef CONFIG_HOTPLUG_SMT
> enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED;
> +static unsigned int cpu_smt_max_threads __ro_after_init;
> +unsigned int cpu_smt_num_threads;
Why needs this to be global? cpu_smt_control is pointlessly global already.
> void __init cpu_smt_disable(bool force)
> {
> @@ -433,10 +435,18 @@ void __init cpu_smt_disable(bool force)
> * The decision whether SMT is supported can only be done after the full
> * CPU identification. Called from architecture code.
> */
> -void __init cpu_smt_check_topology(void)
> +void __init cpu_smt_check_topology(unsigned int num_threads)
> {
> if (!topology_smt_supported())
> cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
> +
> + cpu_smt_max_threads = num_threads;
> +
> + // May already be disabled by nosmt command line parameter
> + if (cpu_smt_control != CPU_SMT_ENABLED)
> + cpu_smt_num_threads = 1;
> + else
> + cpu_smt_num_threads = num_threads;
Taking Laurents findings into account this should be something like
the incomplete below.
x86 would simply invoke cpu_smt_set_num_threads() with both arguments as
smp_num_siblings while PPC can funnel its command line parameter through
the num_threads argument.
Thanks,
tglx
---
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -414,6 +414,8 @@ void __weak arch_smt_update(void) { }
#ifdef CONFIG_HOTPLUG_SMT
enum cpuhp_smt_control cpu_smt_control __read_mostly = CPU_SMT_ENABLED;
+static unsigned int cpu_smt_max_threads __ro_after_init;
+static unsigned int cpu_smt_num_threads = UINT_MAX;
void __init cpu_smt_disable(bool force)
{
@@ -427,24 +429,31 @@ void __init cpu_smt_disable(bool force)
pr_info("SMT: disabled\n");
cpu_smt_control = CPU_SMT_DISABLED;
}
+ cpu_smt_num_threads = 1;
}
/*
* The decision whether SMT is supported can only be done after the full
* CPU identification. Called from architecture code.
*/
-void __init cpu_smt_check_topology(void)
+void __init cpu_smt_set_num_threads(unsigned int max_threads, unsigned int num_threads)
{
- if (!topology_smt_supported())
+ if (max_threads == 1)
cpu_smt_control = CPU_SMT_NOT_SUPPORTED;
-}
-static int __init smt_cmdline_disable(char *str)
-{
- cpu_smt_disable(str && !strcmp(str, "force"));
- return 0;
+ cpu_smt_max_threads = max_threads;
+
+ /*
+ * If SMT has been disabled via the kernel command line or SMT is
+ * not supported, set cpu_smt_num_threads to 1 for consistency.
+ * If enabled, take the architecture requested number of threads
+ * to bring up into account.
+ */
+ if (cpu_smt_control != CPU_SMT_ENABLED)
+ cpu_smt_num_threads = 1;
+ else if (num_threads < cpu_smt_num_threads)
+ cpu_smt_num_threads = num_threads;
}
-early_param("nosmt", smt_cmdline_disable);
static inline bool cpu_smt_allowed(unsigned int cpu)
{
@@ -463,6 +472,13 @@ static inline bool cpu_smt_allowed(unsig
return !cpumask_test_cpu(cpu, &cpus_booted_once_mask);
}
+static int __init smt_cmdline_disable(char *str)
+{
+ cpu_smt_disable(str && !strcmp(str, "force"));
+ return 0;
+}
+early_param("nosmt", smt_cmdline_disable);
+
/* Returns true if SMT is not supported of forcefully (irreversibly) disabled */
bool cpu_smt_possible(void)
{
next prev parent reply other threads:[~2023-06-10 21:27 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 [this message]
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
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
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=87fs6z80w5.ffs@tglx \
--to=tglx@linutronix.de \
--cc=bp@alien8.de \
--cc=dave.hansen@linux.intel.com \
--cc=ldufour@linux.ibm.com \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mingo@redhat.com \
--cc=mpe@ellerman.id.au \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).