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From: Denis Vlasenko <vda@ilport.com.ua>
To: <cutaway@bellsouth.net>, "Jesper Juhl" <juhl-lkml@dif.dk>,
       "linux-kernel" <linux-kernel@vger.kernel.org>
Subject: Re: [RFC] cleanup patches for strings
Date: Tue, 21 Jun 2005 16:20:31 +0300
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Cc: "Andrew Morton" <akpm@osdl.org>, "Jeff Garzik" <jgarzik@pobox.com>,
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References: <Pine.LNX.4.62.0506200052320.2415@dragon.hyggekrogen.localhost> <200506211402.48554.vda@ilport.com.ua> <004c01c57662$5eacc260$2800000a@pc365dualp2>
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Um, prev one was using push %reg. My fault.
push $imm gives the same result:

# gcc -O2 -falign-loops=64 t.c
# ./a.out
Took 9291 CPU cycles Took 8068 CPU cycles
Took 9080 CPU cycles Took 8058 CPU cycles
Took 9134 CPU cycles Took 8061 CPU cycles
Took 9084 CPU cycles Took 8043 CPU cycles
Took 9084 CPU cycles Took 8043 CPU cycles
Took 9084 CPU cycles Took 8043 CPU cycles

The source:

#define rdtscl(low) asm volatile("rdtsc" : "=a" (low) : : "edx")

#define NL "\n"

#include <stdio.h>

int main() {
    int i,k,start,end;
    int v = 1234;

for(k=0; k<6; k++) {
    rdtscl(start);
    for(i=0; i<1000; i++) {
        asm(NL
        "       push    %0" NL
        "       pop     %%eax" NL
        "       push    %0" NL
        "       pop     %%eax" NL
        "       push    %0" NL
        "       pop     %%eax" NL
        "       push    %0" NL
        "       pop     %%eax" NL
        : /* outputs */
        : "m" (v) /* inputs */
        : "ax" /* clobbers */
        );
    }
    rdtscl(end);
    printf("Took %u CPU cycles ", end-start);

    rdtscl(start);
    for(i=0; i<1000; i++) {
        asm(NL
        "       push    $1234" NL
        "       pop     %%eax" NL
        "       push    $1234" NL
        "       pop     %%eax" NL
        "       push    $1234" NL
        "       pop     %%eax" NL
        "       push    $1234" NL
        "       pop     %%eax" NL
        : /* outputs */
        : /* inputs */
        : "ax" /* clobbers */
        );
    }
    rdtscl(end);
    printf("Took %u CPU cycles\n", end-start);
}
    return 0;
}
--
vda