From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 81EE03D5242 for ; Wed, 4 Mar 2026 18:55:35 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772650535; cv=none; b=VxXXJv07PNaLt0dMe6ntEF/Op1v7CI3dmf5EvlDFR1fYmjxb6lvFOuK9so4gxGEVPwoeRwircXtBZaZV3B26wyM30WNTcSdl5kWgnEKCTAVhYIJqJvuNkWLzyv6vqZGyErc/SGJyI7PmpUecDTaOr2eZALPkjcgAs32989GWi1g= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772650535; c=relaxed/simple; bh=5/YJcGbPneiW3axb3xDnS52zu3QFvBBPw24JJ/4Gzu8=; h=Date:Message-ID:From:To:Cc:Subject:References:MIME-Version: Content-Type; b=ejQ73ETKjg2m2XP6g28r377O7vqoXmvs0cV5IvGBKSA6154o5/9Ahe2liLMmsqY3+gbv7UV2p04XtRZJ2jWQBZGm5rXtvS4foauanP9NSPCA5ZzxpRfRfvkUbN0DBKbPVPnXYX9+eDmZlkM89S4KXyCCVHn4DBUMVNZdUAppnFY= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=lUq3mAsk; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="lUq3mAsk" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 64519C2BC86; Wed, 4 Mar 2026 18:55:34 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772650535; bh=5/YJcGbPneiW3axb3xDnS52zu3QFvBBPw24JJ/4Gzu8=; h=Date:From:To:Cc:Subject:References:From; b=lUq3mAskXDnIqXu3KFw0KawWLJYhZSnqR1ot2iXa8nAa8etLBGhZ00rc4nINRTQH8 VfIfP3rFExJh2FxcLLjtGdqzFvO4ertE0h6XK5FnmUesWT8CVXDcF7MuqJUmAv4Gxv /YmO4cDR6sLasgpu1R1xHsXutE6l4Zcf6i2Uqj9cRskedruFYDl78Bx7BnJTv17yWT hYYYA6HdtclNkONDwiPlxFbaCHgquF2gPrZb1o6BKR/T7I0STaIJ+CnD0v0Rcd2MOA yUaCRz/zQZH3qAAWTJevZAYHlhDiiIawQ4K4iJYal0Mzw7XuKvDSg0DUhwzLYtEouP Y6IfhFoTzVmlw== Date: Wed, 04 Mar 2026 19:55:31 +0100 Message-ID: <20260303154548.004368407@kernel.org> User-Agent: quilt/0.68 From: Thomas Gleixner To: LKML Cc: x86@kernel.org, Dmitry Ilvokhin , Neil Horman Subject: [patch 01/14] x86/irq: Optimize interrupts decimals printing References: <20260303150539.513068586@kernel.org> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 From: Dmitry Ilvokhin Monitoring tools periodically scan /proc/interrupts to export metrics as a timeseries for future analysis and investigation. In large fleets, /proc/interrupts is polled (often every few seconds) on every machine. The cumulative overhead adds up quickly across thousands of nodes, so reducing the cost of generating these stats does have a measurable operational impact. With the ongoing trend toward higher core counts per machine, this cost becomes even more noticeable over time, since interrupt counters are per-CPU. In Meta's fleet, we have observed this overhead at scale. Although a binary /proc interface would be a better long-term solution due to lower formatting (kernel side) and parsing (userspace side) overhead, the text interface will remain in use for some time, even if better solutions will be available. Optimizing the /proc/interrupts printing code is therefore still beneficial. Function seq_printf() supports rich format string for decimals printing, but it doesn't required for printing /proc/interrupts per CPU counters, seq_put_decimal_ull_width() function can be used instead to print per CPU counters, because very limited formatting is required for this case. Similar optimization idea is already used in show_interrupts(). Performance counter stats (truncated) for 'sh -c cat /proc/interrupts Before: 3.42 msec task-clock # 0.802 CPUs utilized ( +- 0.05% ) 1 context-switches # 291.991 /sec ( +- 0.74% ) 0 cpu-migrations # 0.000 /sec 343 page-faults # 100.153 K/sec ( +- 0.01% ) 8,932,242 instructions # 1.66 insn per cycle ( +- 0.34% ) 5,374,427 cycles # 1.569 GHz ( +- 0.04% ) 1,483,154 branches # 433.068 M/sec ( +- 0.22% ) 28,768 branch-misses # 1.94% of all branches ( +- 0.31% ) 0.00427182 +- 0.00000215 seconds time elapsed ( +- 0.05% ) After: 2.39 msec task-clock # 0.796 CPUs utilized ( +- 0.06% ) 1 context-switches # 418.541 /sec ( +- 0.70% ) 0 cpu-migrations # 0.000 /sec 343 page-faults # 143.560 K/sec ( +- 0.01% ) 7,020,982 instructions # 1.30 insn per cycle ( +- 0.52% ) 5,397,266 cycles # 2.259 GHz ( +- 0.06% ) 1,569,648 branches # 656.962 M/sec ( +- 0.08% ) 25,419 branch-misses # 1.62% of all branches ( +- 0.72% ) 0.00299996 +- 0.00000206 seconds time elapsed ( +- 0.07% ) Relative speed up in time elapsed is around 29%. [ tglx: Fixed it up so it applies to current mainline ] Signed-off-by: Dmitry Ilvokhin Signed-off-by: Thomas Gleixner Link: https://patch.msgid.link/aQj5mGZ6_BBlAm3B@shell.ilvokhin.com --- Changes v2: - Expanded commit message: add more rationale for the proposed change. - Renamed helper put_spaced_decimal() -> put_decimal() primarely to make checkpatch.pl --strict pass. arch/x86/kernel/irq.c | 112 ++++++++++++++++++++++++++------------------------ 1 file changed, 59 insertions(+), 53 deletions(-) --- a/arch/x86/kernel/irq.c +++ b/arch/x86/kernel/irq.c @@ -62,6 +62,18 @@ void ack_bad_irq(unsigned int irq) apic_eoi(); } +/* + * A helper routine for putting space and decimal number without overhead + * from rich format of printf(). + */ +static void put_decimal(struct seq_file *p, unsigned long long num) +{ + const char *delimiter = " "; + unsigned int width = 10; + + seq_put_decimal_ull_width(p, delimiter, num, width); +} + #define irq_stats(x) (&per_cpu(irq_stat, x)) /* * /proc/interrupts printing for arch specific interrupts @@ -70,103 +82,101 @@ int arch_show_interrupts(struct seq_file { int j; - seq_printf(p, "%*s: ", prec, "NMI"); + seq_printf(p, "%*s:", prec, "NMI"); for_each_online_cpu(j) - seq_printf(p, "%10u ", irq_stats(j)->__nmi_count); + put_decimal(p, irq_stats(j)->__nmi_count); seq_puts(p, " Non-maskable interrupts\n"); #ifdef CONFIG_X86_LOCAL_APIC - seq_printf(p, "%*s: ", prec, "LOC"); + seq_printf(p, "%*s:", prec, "LOC"); for_each_online_cpu(j) - seq_printf(p, "%10u ", irq_stats(j)->apic_timer_irqs); + put_decimal(p, irq_stats(j)->apic_timer_irqs); seq_puts(p, " Local timer interrupts\n"); - seq_printf(p, "%*s: ", prec, "SPU"); + seq_printf(p, "%*s:", prec, "SPU"); for_each_online_cpu(j) - seq_printf(p, "%10u ", irq_stats(j)->irq_spurious_count); + put_decimal(p, irq_stats(j)->irq_spurious_count); seq_puts(p, " Spurious interrupts\n"); - seq_printf(p, "%*s: ", prec, "PMI"); + seq_printf(p, "%*s:", prec, "PMI"); for_each_online_cpu(j) - seq_printf(p, "%10u ", irq_stats(j)->apic_perf_irqs); + put_decimal(p, irq_stats(j)->apic_perf_irqs); seq_puts(p, " Performance monitoring interrupts\n"); - seq_printf(p, "%*s: ", prec, "IWI"); + seq_printf(p, "%*s:", prec, "IWI"); for_each_online_cpu(j) - seq_printf(p, "%10u ", irq_stats(j)->apic_irq_work_irqs); + put_decimal(p, irq_stats(j)->apic_irq_work_irqs); seq_puts(p, " IRQ work interrupts\n"); - seq_printf(p, "%*s: ", prec, "RTR"); + seq_printf(p, "%*s:", prec, "RTR"); for_each_online_cpu(j) - seq_printf(p, "%10u ", irq_stats(j)->icr_read_retry_count); + put_decimal(p, irq_stats(j)->icr_read_retry_count); seq_puts(p, " APIC ICR read retries\n"); if (x86_platform_ipi_callback) { - seq_printf(p, "%*s: ", prec, "PLT"); + seq_printf(p, "%*s:", prec, "PLT"); for_each_online_cpu(j) - seq_printf(p, "%10u ", irq_stats(j)->x86_platform_ipis); + put_decimal(p, irq_stats(j)->x86_platform_ipis); seq_puts(p, " Platform interrupts\n"); } #endif #ifdef CONFIG_SMP - seq_printf(p, "%*s: ", prec, "RES"); + seq_printf(p, "%*s:", prec, "RES"); for_each_online_cpu(j) - seq_printf(p, "%10u ", irq_stats(j)->irq_resched_count); + put_decimal(p, irq_stats(j)->irq_resched_count); seq_puts(p, " Rescheduling interrupts\n"); - seq_printf(p, "%*s: ", prec, "CAL"); + seq_printf(p, "%*s:", prec, "CAL"); for_each_online_cpu(j) - seq_printf(p, "%10u ", irq_stats(j)->irq_call_count); + put_decimal(p, irq_stats(j)->irq_call_count); seq_puts(p, " Function call interrupts\n"); - seq_printf(p, "%*s: ", prec, "TLB"); + seq_printf(p, "%*s:", prec, "TLB"); for_each_online_cpu(j) - seq_printf(p, "%10u ", irq_stats(j)->irq_tlb_count); + put_decimal(p, irq_stats(j)->irq_tlb_count); seq_puts(p, " TLB shootdowns\n"); #endif #ifdef CONFIG_X86_THERMAL_VECTOR - seq_printf(p, "%*s: ", prec, "TRM"); + seq_printf(p, "%*s:", prec, "TRM"); for_each_online_cpu(j) - seq_printf(p, "%10u ", irq_stats(j)->irq_thermal_count); + put_decimal(p, irq_stats(j)->irq_thermal_count); seq_puts(p, " Thermal event interrupts\n"); #endif #ifdef CONFIG_X86_MCE_THRESHOLD - seq_printf(p, "%*s: ", prec, "THR"); + seq_printf(p, "%*s:", prec, "THR"); for_each_online_cpu(j) - seq_printf(p, "%10u ", irq_stats(j)->irq_threshold_count); + put_decimal(p, irq_stats(j)->irq_threshold_count); seq_puts(p, " Threshold APIC interrupts\n"); #endif #ifdef CONFIG_X86_MCE_AMD - seq_printf(p, "%*s: ", prec, "DFR"); + seq_printf(p, "%*s:", prec, "DFR"); for_each_online_cpu(j) - seq_printf(p, "%10u ", irq_stats(j)->irq_deferred_error_count); + put_decimal(p, irq_stats(j)->irq_deferred_error_count); seq_puts(p, " Deferred Error APIC interrupts\n"); #endif #ifdef CONFIG_X86_MCE - seq_printf(p, "%*s: ", prec, "MCE"); + seq_printf(p, "%*s:", prec, "MCE"); for_each_online_cpu(j) - seq_printf(p, "%10u ", per_cpu(mce_exception_count, j)); + put_decimal(p, per_cpu(mce_exception_count, j)); seq_puts(p, " Machine check exceptions\n"); - seq_printf(p, "%*s: ", prec, "MCP"); + seq_printf(p, "%*s:", prec, "MCP"); for_each_online_cpu(j) - seq_printf(p, "%10u ", per_cpu(mce_poll_count, j)); + put_decimal(p, per_cpu(mce_poll_count, j)); seq_puts(p, " Machine check polls\n"); #endif #ifdef CONFIG_X86_HV_CALLBACK_VECTOR if (test_bit(HYPERVISOR_CALLBACK_VECTOR, system_vectors)) { - seq_printf(p, "%*s: ", prec, "HYP"); + seq_printf(p, "%*s:", prec, "HYP"); for_each_online_cpu(j) - seq_printf(p, "%10u ", - irq_stats(j)->irq_hv_callback_count); + put_decimal(p, irq_stats(j)->irq_hv_callback_count); seq_puts(p, " Hypervisor callback interrupts\n"); } #endif #if IS_ENABLED(CONFIG_HYPERV) if (test_bit(HYPERV_REENLIGHTENMENT_VECTOR, system_vectors)) { - seq_printf(p, "%*s: ", prec, "HRE"); + seq_printf(p, "%*s:", prec, "HRE"); for_each_online_cpu(j) - seq_printf(p, "%10u ", - irq_stats(j)->irq_hv_reenlightenment_count); + put_decimal(p, + irq_stats(j)->irq_hv_reenlightenment_count); seq_puts(p, " Hyper-V reenlightenment interrupts\n"); } if (test_bit(HYPERV_STIMER0_VECTOR, system_vectors)) { - seq_printf(p, "%*s: ", prec, "HVS"); + seq_printf(p, "%*s:", prec, "HVS"); for_each_online_cpu(j) - seq_printf(p, "%10u ", - irq_stats(j)->hyperv_stimer0_count); + put_decimal(p, irq_stats(j)->hyperv_stimer0_count); seq_puts(p, " Hyper-V stimer0 interrupts\n"); } #endif @@ -175,35 +185,31 @@ int arch_show_interrupts(struct seq_file seq_printf(p, "%*s: %10u\n", prec, "MIS", atomic_read(&irq_mis_count)); #endif #if IS_ENABLED(CONFIG_KVM) - seq_printf(p, "%*s: ", prec, "PIN"); + seq_printf(p, "%*s:", prec, "PIN"); for_each_online_cpu(j) - seq_printf(p, "%10u ", irq_stats(j)->kvm_posted_intr_ipis); + put_decimal(p, irq_stats(j)->kvm_posted_intr_ipis); seq_puts(p, " Posted-interrupt notification event\n"); - seq_printf(p, "%*s: ", prec, "NPI"); + seq_printf(p, "%*s:", prec, "NPI"); for_each_online_cpu(j) - seq_printf(p, "%10u ", - irq_stats(j)->kvm_posted_intr_nested_ipis); + put_decimal(p, irq_stats(j)->kvm_posted_intr_nested_ipis); seq_puts(p, " Nested posted-interrupt event\n"); - seq_printf(p, "%*s: ", prec, "PIW"); + seq_printf(p, "%*s:", prec, "PIW"); for_each_online_cpu(j) - seq_printf(p, "%10u ", - irq_stats(j)->kvm_posted_intr_wakeup_ipis); + put_decimal(p, irq_stats(j)->kvm_posted_intr_wakeup_ipis); seq_puts(p, " Posted-interrupt wakeup event\n"); #endif #ifdef CONFIG_GUEST_PERF_EVENTS - seq_printf(p, "%*s: ", prec, "VPMI"); + seq_printf(p, "%*s:", prec, "VPMI"); for_each_online_cpu(j) - seq_printf(p, "%10u ", - irq_stats(j)->perf_guest_mediated_pmis); + put_decimal(p, irq_stats(j)->perf_guest_mediated_pmis); seq_puts(p, " Perf Guest Mediated PMI\n"); #endif #ifdef CONFIG_X86_POSTED_MSI - seq_printf(p, "%*s: ", prec, "PMN"); + seq_printf(p, "%*s:", prec, "PMN"); for_each_online_cpu(j) - seq_printf(p, "%10u ", - irq_stats(j)->posted_msi_notification_count); + put_decimal(p, irq_stats(j)->posted_msi_notification_count); seq_puts(p, " Posted MSI notification event\n"); #endif return 0;