Re: [PATCH v2 net-next] inet: Get critical word in first 64bit of cache line

Ling Ma
2013-02-04T02:53:10Z

[-- Attachment #1: Type: text/plain, Size: 4551 bytes --]

I attached my test program(we force all cpu loads issue one by one ,
and avoid cpu hardwre prefetch cc -o test-cwf test-cwf.c.) and
cpu-info, the result from ./test-cwf indicates as below:
looking-up aligned time 157000272, looking-up unaligned time 162652724
If I was wrong please correct me.

Thanks
Ling

2013/2/4, Eric Dumazet <eric.dumazet@gmail.com>:
> On Sun, 2013-02-03 at 16:18 -0800, Eric Dumazet wrote:
>> On Sun, 2013-02-03 at 16:08 -0500, David Miller wrote:
>> > From: Eric Dumazet <eric.dumazet@gmail.com>
>> > Date: Sat, 02 Feb 2013 07:03:55 -0800
>> >
>> > > From: Ma Ling <ling.ma.program@gmail.com>
>> > >
>> > > In order to reduce memory latency when last level cache miss occurs,
>> > > modern CPUs i.e. x86 and arm introduced Critical Word First(CWF) or
>> > > Early Restart(ER) to get data ASAP. For CWF if critical word is first
>> > > member
>> > > in cache line, memory feed CPU with critical word, then fill others
>> > > data in cache line one by one, otherwise after critical word it must
>> > > cost more cycle to fill the remaining cache line. For Early First CPU
>> > > will restart until critical word in cache line reaches.
>> > >
>> > > Hash value is critical word, so in this patch we place it as first
>> > > member in cache line (sock address is cache-line aligned), and it is
>> > > also good for Early Restart platform as well .
>> > >
>> > > [edumazet: respin on net-next after commit ce43b03e8889]
>> > >
>> > > Signed-off-by: Ma Ling <ling.ma.program@gmail.com>
>> > > Signed-off-by: Eric Dumazet <edumazet@google.com>
>> >
>> > I completely agree with the other response to this patch in that
>> > the description is bogus.
>> >
>> > If CWF is implemented in the cpu, it should exactly relieve us from
>> > having to move things around in structures so carefully like this.
>> >
>> > Either the patch should be completely dropped (modern cpus don't
>> > need this) or the commit message changed to reflect reality.
>> >
>> > It really makes a terrible impression upon me when the patch says
>> > something which in fact is 180 degrees from reality.
>>
>> Hmm.
>>
>> Maybe the changelog is misleading, or maybe all the performance gains I
>> have from this patch are probably some artifact or old/bad hardware, or
>> something else.
>>
>>
>>
>> (Intel(R) Xeon(R) CPU X5660 @ 2.80GHz)
>> # ./cwf
>> looking-up aligned time 108712072,
>> looking-up unaligned time 113268256
>> looking-up aligned time 108677032,
>> looking-up unaligned time 113297636
>>
>>
>> (Intel(R) Xeon(R) CPU X5679 @ 3.20GHz)
>> # ./cwf
>> looking-up aligned time 139193589,
>> looking-up unaligned time 144307821
>> looking-up aligned time 139136787,
>> looking-up unaligned time 144277752
>>
>> My laptop : Intel(R) Core(TM) i5-2520M CPU @ 2.50GHz
>> # ./cwf
>> looking-up aligned time 84869203,
>> looking-up unaligned time 86843462
>> looking-up aligned time 84253003,
>> looking-up unaligned time 86227675
>>
>> #include <stdio.h>
>> #include <string.h>
>> #include <stdlib.h>
>> #include <unistd.h>
>>
>> #define CACHELINE_SZ 64L
>>
>> #define BIGBUFFER_SZ (64<<20)
>>
>> # define HP_TIMING_NOW(Var) \
>> ({ unsigned long long _hi, _lo; \
>> asm volatile ("rdtsc" : "=a" (_lo), "=d" (_hi)); \
>> (Var) = _hi << 32 | _lo; })
>>
>> #define repeat_times 20
>>
>> char *bufzap;
>>
>> static void zap_cache(void)
>> {
>> memset(bufzap, 2, BIGBUFFER_SZ);
>> memset(bufzap, 3, BIGBUFFER_SZ);
>> memset(bufzap, 4, BIGBUFFER_SZ);
>> }
>>
>> static char *init_buf(void)
>> {
>> void *res;
>>
>> if (posix_memalign(&res, CACHELINE_SZ, BIGBUFFER_SZ)) {
>> fprintf(stderr, "malloc() failed");
>> exit(1);
>> }
>>
>> memset(res, 1, BIGBUFFER_SZ);
>> return res;
>> }
>>
>> unsigned long total;
>>
>> static unsigned long random_access(void *buffer,
>> unsigned int off1,
>> unsigned int off2,
>> unsigned int off3)
>> {
>> int i;
>> unsigned int n;
>> unsigned long sum = 0;
>> unsigned long *ptr;
>>
>> srandom(7777);
>> for (i = 0; i < 1000000; i++) {
>> n = random() % (BIGBUFFER_SZ/CACHELINE_SZ);
>> ptr = buffer + n*CACHELINE_SZ;
>> if (ptr[off1])
>> sum++;
>> if (ptr[off2])
>> sum++;
>> // if (ptr[off3])
>> // sum++;
>
> Hmm, I don't know why I left a comment on these two lines...
>
> Of course, results are a bit different removing the comments :
>
> looking-up aligned time 113601316,
> looking-up unaligned time 115964760
> looking-up aligned time 113698636,
> looking-up unaligned time 115986072
>
> More testing is probably needed.
>
>
>

[-- Attachment #2: cpu-info --]
[-- Type: text/plain, Size: 7050 bytes --]

processor : 0
vendor_id : GenuineIntel
cpu family : 6
model : 44
model name : Intel(R) Xeon(R) CPU E5620 @ 2.40GHz
stepping : 2
microcode : 0x10
cpu MHz : 2400.153
cache size : 12288 KB
physical id : 0
siblings : 8
core id : 0
cpu cores : 4
apicid : 0
initial apicid : 0
fpu : yes
fpu_exception : yes
cpuid level : 11
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 popcnt aes lahf_lm arat epb dtherm tpr_shadow vnmi flexpriority ept vpid
bogomips : 4800.30
clflush size : 64
cache_alignment : 64
address sizes : 40 bits physical, 48 bits virtual
power management:

processor : 1
vendor_id : GenuineIntel
cpu family : 6
model : 44
model name : Intel(R) Xeon(R) CPU E5620 @ 2.40GHz
stepping : 2
microcode : 0x10
cpu MHz : 2400.153
cache size : 12288 KB
physical id : 0
siblings : 8
core id : 1
cpu cores : 4
apicid : 2
initial apicid : 2
fpu : yes
fpu_exception : yes
cpuid level : 11
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 popcnt aes lahf_lm arat epb dtherm tpr_shadow vnmi flexpriority ept vpid
bogomips : 4800.30
clflush size : 64
cache_alignment : 64
address sizes : 40 bits physical, 48 bits virtual
power management:

processor : 2
vendor_id : GenuineIntel
cpu family : 6
model : 44
model name : Intel(R) Xeon(R) CPU E5620 @ 2.40GHz
stepping : 2
microcode : 0x10
cpu MHz : 2400.153
cache size : 12288 KB
physical id : 0
siblings : 8
core id : 9
cpu cores : 4
apicid : 18
initial apicid : 18
fpu : yes
fpu_exception : yes
cpuid level : 11
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 popcnt aes lahf_lm arat epb dtherm tpr_shadow vnmi flexpriority ept vpid
bogomips : 4800.30
clflush size : 64
cache_alignment : 64
address sizes : 40 bits physical, 48 bits virtual
power management:

processor : 3
vendor_id : GenuineIntel
cpu family : 6
model : 44
model name : Intel(R) Xeon(R) CPU E5620 @ 2.40GHz
stepping : 2
microcode : 0x10
cpu MHz : 2400.153
cache size : 12288 KB
physical id : 0
siblings : 8
core id : 10
cpu cores : 4
apicid : 20
initial apicid : 20
fpu : yes
fpu_exception : yes
cpuid level : 11
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 popcnt aes lahf_lm arat epb dtherm tpr_shadow vnmi flexpriority ept vpid
bogomips : 4800.30
clflush size : 64
cache_alignment : 64
address sizes : 40 bits physical, 48 bits virtual
power management:

processor : 4
vendor_id : GenuineIntel
cpu family : 6
model : 44
model name : Intel(R) Xeon(R) CPU E5620 @ 2.40GHz
stepping : 2
microcode : 0x10
cpu MHz : 2400.153
cache size : 12288 KB
physical id : 0
siblings : 8
core id : 0
cpu cores : 4
apicid : 1
initial apicid : 1
fpu : yes
fpu_exception : yes
cpuid level : 11
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 popcnt aes lahf_lm arat epb dtherm tpr_shadow vnmi flexpriority ept vpid
bogomips : 4800.30
clflush size : 64
cache_alignment : 64
address sizes : 40 bits physical, 48 bits virtual
power management:

processor : 5
vendor_id : GenuineIntel
cpu family : 6
model : 44
model name : Intel(R) Xeon(R) CPU E5620 @ 2.40GHz
stepping : 2
microcode : 0x10
cpu MHz : 2400.153
cache size : 12288 KB
physical id : 0
siblings : 8
core id : 1
cpu cores : 4
apicid : 3
initial apicid : 3
fpu : yes
fpu_exception : yes
cpuid level : 11
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 popcnt aes lahf_lm arat epb dtherm tpr_shadow vnmi flexpriority ept vpid
bogomips : 4800.30
clflush size : 64
cache_alignment : 64
address sizes : 40 bits physical, 48 bits virtual
power management:

processor : 6
vendor_id : GenuineIntel
cpu family : 6
model : 44
model name : Intel(R) Xeon(R) CPU E5620 @ 2.40GHz
stepping : 2
microcode : 0x10
cpu MHz : 2400.153
cache size : 12288 KB
physical id : 0
siblings : 8
core id : 9
cpu cores : 4
apicid : 19
initial apicid : 19
fpu : yes
fpu_exception : yes
cpuid level : 11
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 popcnt aes lahf_lm arat epb dtherm tpr_shadow vnmi flexpriority ept vpid
bogomips : 4800.30
clflush size : 64
cache_alignment : 64
address sizes : 40 bits physical, 48 bits virtual
power management:

processor : 7
vendor_id : GenuineIntel
cpu family : 6
model : 44
model name : Intel(R) Xeon(R) CPU E5620 @ 2.40GHz
stepping : 2
microcode : 0x10
cpu MHz : 2400.153
cache size : 12288 KB
physical id : 0
siblings : 8
core id : 10
cpu cores : 4
apicid : 21
initial apicid : 21
fpu : yes
fpu_exception : yes
cpuid level : 11
wp : yes
flags : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf pni pclmulqdq dtes64 monitor ds_cpl vmx smx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 popcnt aes lahf_lm arat epb dtherm tpr_shadow vnmi flexpriority ept vpid
bogomips : 4800.30
clflush size : 64
cache_alignment : 64
address sizes : 40 bits physical, 48 bits virtual
power management:

[-- Attachment #3: test-cwf.c --]
[-- Type: text/x-csrc, Size: 1986 bytes --]

#include<stdio.h>
#include<string.h>
#include<stdlib.h>
#include<unistd.h>
#define MAX_BUF_NUM (1 << 20)
#define MAX_BUF_SIZE (1 << 8)
#define ACCESS_OFFSET (0x38)

# define HP_TIMING_NOW(Var) \
({ unsigned long long _hi, _lo; \
asm volatile ("rdtsc" : "=a" (_lo), "=d" (_hi)); \
(Var) = _hi << 32 | _lo; })

#define repeat_times (64)

static void init_buf(char **buf)
{
int i = 0;
char *start;
char *end;
int pagesize = getpagesize();
*buf = malloc(MAX_BUF_SIZE * MAX_BUF_NUM + pagesize);
if(*buf == NULL) {
printf("\nfait to malloc space!\n");
exit(1);
} else {
*buf = *buf + pagesize;
*buf = (char *)(((unsigned long)*buf) & (-pagesize));
}

start = *buf;
end = *buf + (MAX_BUF_SIZE * MAX_BUF_NUM) - MAX_BUF_SIZE;

while(1) {
*((unsigned char **)start) = end;
*((unsigned char **)(start + ACCESS_OFFSET)) = (end + ACCESS_OFFSET);
start = start + MAX_BUF_SIZE;
if(start == end)
break;
*((unsigned char **)end) = start;
*((unsigned char **)(end + ACCESS_OFFSET)) = start + ACCESS_OFFSET;
end = end - MAX_BUF_SIZE;
}

}

unsigned long lookingup_memmory(char *access, int num)
{
__asm__("sub $1, %rsi");
__asm__("xor %rax, %rax");
__asm__("1:");
__asm__("mov (%rdi), %r8");
__asm__("add %r8, %rax");
__asm__("mov %r8, %rdi");
__asm__("sub $1, %rsi");
__asm__("jae 1b");
}

static unsigned long test_lookup_time(char *buf)
{
unsigned long i, start, end, best_time = ~0;

for(i = 0; i < repeat_times; i++) {
HP_TIMING_NOW(start);
lookingup_memmory(buf, MAX_BUF_NUM);
HP_TIMING_NOW(end);
if(best_time > (end - start))
best_time = (end - start);
}

return best_time;

}
void main (void)
{
char *buf1 = NULL;
char *buf2 = NULL;
unsigned long aligned_time, unaligned_time;

init_buf(&buf1);
init_buf(&buf2);

unaligned_time = test_lookup_time(buf2 + ACCESS_OFFSET);
aligned_time = test_lookup_time(buf1);

printf("looking-up aligned time %ld, looking-up unaligned time %ld\n", aligned_time, unaligned_time);
}