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Re: partially uptodate page reads

To: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>, Christoph Hellwig <hch@xxxxxxxxxxxxx>
Subject: Re: partially uptodate page reads
From: Hisashi Hifumi <hifumi.hisashi@xxxxxxxxxxxxx>
Date: Mon, 28 Jul 2008 13:34:12 +0900
Cc: Nick Piggin <nickpiggin@xxxxxxxxxxxx>, jack@xxxxxx, linux-ext4@xxxxxxxxxxxxxxx, linux-fsdevel@xxxxxxxxxxxxxxx, xfs@xxxxxxxxxxx
In-reply-to: <20080724120841.81c72be9.akpm@xxxxxxxxxxxxxxxxxxxx>
References: <200807250117.11331.nickpiggin@xxxxxxxxxxxx> <20080724175913.GA32117@xxxxxxxxxxxxx> <20080724120841.81c72be9.akpm@xxxxxxxxxxxxxxxxxxxx>
Sender: xfs-bounce@xxxxxxxxxxx
Hi

>> > 
>> > Are there significant numbers of people using block size < page size in
>> > situations where performance is important and significantly improved by
>> > this patch? Can you give any performance numbers to illustrate perhaps?
>> 
>> With XFS lots of people use 4k blocksize filesystems on ia64 systems
>> with 16k pages, so an optimization like this would be useful.
>
>As Nick says, we really should have some measurement results which
>confirm this theory.  Maybe we did do some but they didn't find theor
>way into the changelog.
>
>I've put the patch on hold until this confirmation data is available.
>

I've got some performance number.
I wrote a benchmark program and got result number with this program.
This benchmark do:
        1, mount and open a test file.
        2, create a 512MB file.
        3, close a file and umount.
        4, mount and again open a test file.
        5, pwrite randomly 300000 times on a test file. offset is aligned by IO 
size(1024bytes).
        6, measure time of preading randomly 100000 times on a test file.

The result was:
        2.6.26
        330 sec

        2.6.26-patched
        226 sec

Arch:i386 
Filesystem:ext3
Blocksize:1024 bytes
Memory: 1GB

On ext3/4, a file is written through buffer/block. So random read/write mixed 
workloads
or random read after random write workloads are optimized with this patch under 
pagesize != blocksize environment. This test result showed this.


The benchmark program is as follows:

#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
#include <unistd.h>
#include <time.h>
#include <stdlib.h>
#include <string.h>
#include <sys/mount.h>

#define LEN 1024
#define LOOP 1024*512 /* 512MB */

main(void)
{
        unsigned long i, offset, filesize;
        int fd;
        char buf[LEN];
        time_t t1, t2;

        if (mount("/dev/sda1", "/root/test1/", "ext3", 0, 0) < 0) {
                perror("cannot mount\n");
                exit(1);
        }
        memset(buf, 0, LEN);
        fd = open("/root/test1/testfile", O_CREAT|O_RDWR|O_TRUNC);
        if (fd < 0) {
                perror("cannot open file\n");
                exit(1);
        }
        for (i = 0; i < LOOP; i++)
                write(fd, buf, LEN);
        close(fd);
        if (umount("/root/test1/") < 0) {
                perror("cannot umount\n");
                exit(1);
        }
        if (mount("/dev/sda1", "/root/test1/", "ext3", 0, 0) < 0) {
                perror("cannot mount\n");
                exit(1);
        }
        fd = open("/root/test1/testfile", O_RDWR);
        if (fd < 0) {
                perror("cannot open file\n");
                exit(1);
        }

        filesize = LEN * LOOP;
        for (i = 0; i < 300000; i++){
                offset = (random() % filesize) & (~(LEN - 1));
                pwrite(fd, buf, LEN, offset);
        }
        printf("start test\n");
        time(&t1);
        for (i = 0; i < 100000; i++){
                offset = (random() % filesize) & (~(LEN - 1));
                pread(fd, buf, LEN, offset);
        }
        time(&t2);
        printf("%ld sec\n", t2-t1);
        close(fd);
        if (umount("/root/test1/") < 0) {
                perror("cannot umount\n");
                exit(1);
        }
}


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