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Message-Id: <20240325035102.15245-1-adrianhuang0701@gmail.com>
Date: Mon, 25 Mar 2024 11:51:02 +0800
From: Adrian Huang <adrianhuang0701@...il.com>
To: Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org,
Adrian Huang <adrianhuang0701@...il.com>,
Jiwei Sun <sunjw10@...ovo.com>,
Adrian Huang <ahuang12@...ovo.com>
Subject: [PATCH 1/1] genirq/proc: Try to jump over the unallocated irq hole whenever possible
From: Adrian Huang <ahuang12@...ovo.com>
Current approach blindly iterates the irq number until the number is
greater than 'nr_irqs', and checks if each irq is allocated.
Here is an example:
* 2-socket server with 488 cores (HT-enabled).
* The last allocated irq is 508. [1]
* nr_irqs = 8360. The following is from dmesg.
NR_IRQS: 524544, nr_irqs: 8360, preallocated irqs: 16
7852 iterations (8360 - 509 + 1) are not necessary. And, there
are some irq unallocated holes from irq 0-508. [1]
The solution is to try jumping over the unallocated irq hole when an
unallocated irq is detected.
Test Result
-----------
* The following ftrace log makes sure that this patch jumps over the
unallocated irq hole (less seq_read_iter() works).
** ftrace w/ patch:
| seq_read_iter() {
+---2230 lines: 0.791 us | mutex_lock();------------
| seq_read_iter() {
0.621 us | mutex_lock();
0.391 us | int_seq_start();
0.411 us | int_seq_stop();
0.391 us | mutex_unlock();
3.916 us | }
** ftrace wo/ patch:
| seq_read_iter() {
+--17955 lines: 0.722 us | mutex_lock();------------
| seq_read_iter() {
0.621 us | mutex_lock();
0.400 us | int_seq_start();
0.380 us | int_seq_stop();
0.381 us | mutex_unlock();
3.946 us | }
* The following result is the average execution time of five-time
measurements about seq_read_iter().
no patch (us) patched (us) saved
------------- ------------ -------
158552 148094 6.6%
[1] https://gist.github.com/AdrianHuang/6c60b8053b2b3ecf6da56dec7a0eae70
Tested-by: Jiwei Sun <sunjw10@...ovo.com>
Signed-off-by: Adrian Huang <ahuang12@...ovo.com>
---
kernel/irq/proc.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/kernel/irq/proc.c b/kernel/irq/proc.c
index 623b8136e9af..756bdc1fd07b 100644
--- a/kernel/irq/proc.c
+++ b/kernel/irq/proc.c
@@ -485,7 +485,14 @@ int show_interrupts(struct seq_file *p, void *v)
rcu_read_lock();
desc = irq_to_desc(i);
- if (!desc || irq_settings_is_hidden(desc))
+ if (!desc) {
+ /* Try to jump over the unallocated irq hole. */
+ *(int *) v = irq_get_next_irq(i + 1) - 1;
+
+ goto outsparse;
+ }
+
+ if (irq_settings_is_hidden(desc))
goto outsparse;
if (desc->kstat_irqs) {
--
2.25.1
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