From: Thomas Gleixner <tglx@kernel.org>
To: LKML <linux-kernel@vger.kernel.org>
Cc: x86@kernel.org, Dmitry Ilvokhin <d@ilvokhin.com>,
Neil Horman <nhorman@tuxdriver.com>
Subject: [patch 01/14] x86/irq: Optimize interrupts decimals printing
Date: Wed, 04 Mar 2026 19:55:31 +0100 [thread overview]
Message-ID: <20260303154548.004368407@kernel.org> (raw)
In-Reply-To: 20260303150539.513068586@kernel.org
From: Dmitry Ilvokhin <d@ilvokhin.com>
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 <d@ilvokhin.com>
Signed-off-by: Thomas Gleixner <tglx@kernel.org>
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;
next prev parent reply other threads:[~2026-03-04 18:55 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-03-04 18:55 [patch 00/14] genirq: Improve /proc/interrupts for real and add a binary interface Thomas Gleixner
2026-03-04 18:55 ` Thomas Gleixner [this message]
2026-03-04 18:55 ` [patch 02/14] genirq/proc: Avoid formatting zero counts in /proc/interrupts Thomas Gleixner
2026-03-09 15:59 ` Dmitry Ilvokhin
2026-03-04 18:55 ` [patch 03/14] genirq/proc: Utilize irq_desc::tot_count to avoid evaluation Thomas Gleixner
2026-03-09 16:04 ` Dmitry Ilvokhin
2026-03-04 18:55 ` [patch 04/14] x86/irq: Make irqstats array based Thomas Gleixner
2026-03-04 22:18 ` Michael Kelley
2026-03-05 15:52 ` Thomas Gleixner
2026-03-09 18:12 ` Dmitry Ilvokhin
2026-03-10 10:15 ` Thomas Gleixner
2026-03-04 18:55 ` [patch 05/14] genirq: Expose nr_irqs in core code Thomas Gleixner
2026-03-09 18:26 ` Dmitry Ilvokhin
2026-03-04 18:55 ` [patch 06/14] genirq: Cache the condition for /proc/interrupts exposure Thomas Gleixner
2026-03-16 18:46 ` Dmitry Ilvokhin
2026-03-04 18:55 ` [patch 07/14] genirq: Calculate precision only when required Thomas Gleixner
2026-03-16 18:57 ` Dmitry Ilvokhin
2026-03-04 18:56 ` [patch 08/14] genirq: Add rcuref count to struct irq_desc Thomas Gleixner
2026-03-04 18:56 ` [patch 09/14] genirq: Expose irq_find_desc_at_or_after() in core code Thomas Gleixner
2026-03-04 18:56 ` [patch 10/14] genirq/proc: Speed up /proc/interrupts iteration Thomas Gleixner
2026-03-04 18:56 ` [patch 11/14] [RFC] genirq: Cache target CPU for single CPU affinities Thomas Gleixner
2026-03-04 18:56 ` [patch 12/14] [RFC] genirq/proc: Provide binary statistic interface Thomas Gleixner
2026-03-04 18:56 ` [patch 13/14] [RFC] genirq/proc: Provide architecture specific binary statistics Thomas Gleixner
2026-03-04 18:56 ` [patch 14/14] [RFC] x86/irq: Hook up architecture specific stats Thomas Gleixner
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=20260303154548.004368407@kernel.org \
--to=tglx@kernel.org \
--cc=d@ilvokhin.com \
--cc=linux-kernel@vger.kernel.org \
--cc=nhorman@tuxdriver.com \
--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