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Piccoli" , x86@kernel.org, linux-kernel@vger.kernel.org In-Reply-To: <20230512205256.148255496@linutronix.de> References: <20230512205256.148255496@linutronix.de> MIME-Version: 1.0 Message-ID: <168422820027.404.885982874682038365.tip-bot2@tip-bot2> Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails X-Spam-Status: No, score=-4.4 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,RCVD_IN_DNSWL_MED,SPF_HELO_NONE, SPF_PASS,T_SCC_BODY_TEXT_LINE,URIBL_BLOCKED autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-getmail-retrieved-from-mailbox: =?utf-8?q?INBOX?= X-GMAIL-THRID: =?utf-8?q?1765724765759957138?= X-GMAIL-MSGID: =?utf-8?q?1766041457749084418?= The following commit has been merged into the smp/core branch of tip: Commit-ID: 9d349d47f0e39b4d1b68793ded2459daa1f948f0 Gitweb: https://git.kernel.org/tip/9d349d47f0e39b4d1b68793ded2459daa1f948f0 Author: Thomas Gleixner AuthorDate: Fri, 12 May 2023 23:07:17 +02:00 Committer: Peter Zijlstra CommitterDate: Mon, 15 May 2023 13:44:53 +02:00 x86/smpboot: Make TSC synchronization function call based Spin-waiting on the control CPU until the AP reaches the TSC synchronization is just a waste especially in the case that there is no synchronization required. As the synchronization has to run with interrupts disabled the control CPU part can just be done from a SMP function call. The upcoming AP issues that call async only in the case that synchronization is required. Signed-off-by: Thomas Gleixner Signed-off-by: Peter Zijlstra (Intel) Tested-by: Michael Kelley Tested-by: Oleksandr Natalenko Tested-by: Helge Deller # parisc Tested-by: Guilherme G. Piccoli # Steam Deck Link: https://lore.kernel.org/r/20230512205256.148255496@linutronix.de --- arch/x86/include/asm/tsc.h | 2 -- arch/x86/kernel/smpboot.c | 20 +++----------------- arch/x86/kernel/tsc_sync.c | 36 +++++++++++------------------------- 3 files changed, 14 insertions(+), 44 deletions(-) diff --git a/arch/x86/include/asm/tsc.h b/arch/x86/include/asm/tsc.h index fbdc3d9..dc1b03b 100644 --- a/arch/x86/include/asm/tsc.h +++ b/arch/x86/include/asm/tsc.h @@ -55,12 +55,10 @@ extern bool tsc_async_resets; #ifdef CONFIG_X86_TSC extern bool tsc_store_and_check_tsc_adjust(bool bootcpu); extern void tsc_verify_tsc_adjust(bool resume); -extern void check_tsc_sync_source(int cpu); extern void check_tsc_sync_target(void); #else static inline bool tsc_store_and_check_tsc_adjust(bool bootcpu) { return false; } static inline void tsc_verify_tsc_adjust(bool resume) { } -static inline void check_tsc_sync_source(int cpu) { } static inline void check_tsc_sync_target(void) { } #endif diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c index 8b07c6e..b2f44a8 100644 --- a/arch/x86/kernel/smpboot.c +++ b/arch/x86/kernel/smpboot.c @@ -275,11 +275,7 @@ static void notrace start_secondary(void *unused) */ smp_callin(); - /* - * Check TSC synchronization with the control CPU, which will do - * its part of this from wait_cpu_online(), making it an implicit - * synchronization point. - */ + /* Check TSC synchronization with the control CPU. */ check_tsc_sync_target(); /* @@ -1141,21 +1137,11 @@ static void wait_cpu_callin(unsigned int cpu) } /* - * Bringup step four: Synchronize the TSC and wait for the target AP - * to reach set_cpu_online() in start_secondary(). + * Bringup step four: Wait for the target AP to reach set_cpu_online() in + * start_secondary(). */ static void wait_cpu_online(unsigned int cpu) { - unsigned long flags; - - /* - * Check TSC synchronization with the AP (keep irqs disabled - * while doing so): - */ - local_irq_save(flags); - check_tsc_sync_source(cpu); - local_irq_restore(flags); - /* * Wait for the AP to mark itself online, so the core caller * can drop sparse_irq_lock. diff --git a/arch/x86/kernel/tsc_sync.c b/arch/x86/kernel/tsc_sync.c index 9452dc9..bbc440c 100644 --- a/arch/x86/kernel/tsc_sync.c +++ b/arch/x86/kernel/tsc_sync.c @@ -245,7 +245,6 @@ bool tsc_store_and_check_tsc_adjust(bool bootcpu) */ static atomic_t start_count; static atomic_t stop_count; -static atomic_t skip_test; static atomic_t test_runs; /* @@ -344,21 +343,14 @@ static inline unsigned int loop_timeout(int cpu) } /* - * Source CPU calls into this - it waits for the freshly booted - * target CPU to arrive and then starts the measurement: + * The freshly booted CPU initiates this via an async SMP function call. */ -void check_tsc_sync_source(int cpu) +static void check_tsc_sync_source(void *__cpu) { + unsigned int cpu = (unsigned long)__cpu; int cpus = 2; /* - * No need to check if we already know that the TSC is not - * synchronized or if we have no TSC. - */ - if (unsynchronized_tsc()) - return; - - /* * Set the maximum number of test runs to * 1 if the CPU does not provide the TSC_ADJUST MSR * 3 if the MSR is available, so the target can try to adjust @@ -368,16 +360,9 @@ void check_tsc_sync_source(int cpu) else atomic_set(&test_runs, 3); retry: - /* - * Wait for the target to start or to skip the test: - */ - while (atomic_read(&start_count) != cpus - 1) { - if (atomic_read(&skip_test) > 0) { - atomic_set(&skip_test, 0); - return; - } + /* Wait for the target to start. */ + while (atomic_read(&start_count) != cpus - 1) cpu_relax(); - } /* * Trigger the target to continue into the measurement too: @@ -397,14 +382,14 @@ retry: if (!nr_warps) { atomic_set(&test_runs, 0); - pr_debug("TSC synchronization [CPU#%d -> CPU#%d]: passed\n", + pr_debug("TSC synchronization [CPU#%d -> CPU#%u]: passed\n", smp_processor_id(), cpu); } else if (atomic_dec_and_test(&test_runs) || random_warps) { /* Force it to 0 if random warps brought us here */ atomic_set(&test_runs, 0); - pr_warn("TSC synchronization [CPU#%d -> CPU#%d]:\n", + pr_warn("TSC synchronization [CPU#%d -> CPU#%u]:\n", smp_processor_id(), cpu); pr_warn("Measured %Ld cycles TSC warp between CPUs, " "turning off TSC clock.\n", max_warp); @@ -457,11 +442,12 @@ void check_tsc_sync_target(void) * SoCs the TSC is frequency synchronized, but still the TSC ADJUST * register might have been wreckaged by the BIOS.. */ - if (tsc_store_and_check_tsc_adjust(false) || tsc_clocksource_reliable) { - atomic_inc(&skip_test); + if (tsc_store_and_check_tsc_adjust(false) || tsc_clocksource_reliable) return; - } + /* Kick the control CPU into the TSC synchronization function */ + smp_call_function_single(cpumask_first(cpu_online_mask), check_tsc_sync_source, + (unsigned long *)(unsigned long)cpu, 0); retry: /* * Register this CPU's participation and wait for the