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80e4e1f472
A dsb(ishst) barrier should be enough to order previous writes with
the system register generating the SGI, as we only need to guarantee
the visibility of data to other CPUs in the inner shareable domain
before we send the SGI.
A micro-benchmark is written to verify the performance impact on
kunpeng920 machine with 2 sockets, each socket has 2 dies, and
each die has 24 CPUs, so totally the system has 2 * 2 * 24 = 96
CPUs. ~2% performance improvement can be seen by this benchmark.
The code of benchmark module:
#include <linux/module.h>
#include <linux/timekeeping.h>
volatile int data0 ____cacheline_aligned;
volatile int data1 ____cacheline_aligned;
volatile int data2 ____cacheline_aligned;
volatile int data3 ____cacheline_aligned;
volatile int data4 ____cacheline_aligned;
volatile int data5 ____cacheline_aligned;
volatile int data6 ____cacheline_aligned;
static void ipi_latency_func(void *val)
{
}
static int __init ipi_latency_init(void)
{
ktime_t stime, etime, delta;
int cpu, i;
int start = smp_processor_id();
stime = ktime_get();
for ( i = 0; i < 1000; i++)
for (cpu = 0; cpu < 96; cpu++) {
data0 = data1 = data2 = data3 = data4 = data5 = data6 = cpu;
smp_call_function_single(cpu, ipi_latency_func, NULL, 1);
}
etime = ktime_get();
delta = ktime_sub(etime, stime);
printk("%s ipi from cpu%d to cpu0-95 delta of 1000times:%lld\n",
__func__, start, delta);
return 0;
}
module_init(ipi_latency_init);
static void ipi_latency_exit(void)
{
}
module_exit(ipi_latency_exit);
MODULE_DESCRIPTION("IPI benchmark");
MODULE_LICENSE("GPL");
run the below commands 10 times on both Vanilla and the kernel with this
patch:
# taskset -c 0 insmod test.ko
# rmmod test
The result on vanilla:
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:126757449
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:126784249
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:126177703
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:127022281
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:126184883
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:127374585
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:125778089
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:126974441
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:127357625
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:126228184
The result on the kernel with this patch:
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:124467401
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:123474209
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:123558497
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:122993951
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:122984223
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:123323609
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:124507583
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:123386963
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:123340664
ipi_latency_init ipi from cpu0 to cpu0-95 delta of 1000times:123285324
Signed-off-by: Barry Song <song.bao.hua@hisilicon.com>
[maz: tidied up commit message]
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20220220061910.6155-1-21cnbao@gmail.com
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.