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    Subject[PATCH] 2.5: push BKL out of llseek
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    This patch pushes the BKL out of llseek() and into the individual llseek
    methods. For generic_file_llseek, I replaced it with the inode
    semaphore. The lock contention is noticeable even on 2-way systems.
    Since we simply push the BKL further down the call chain (its the llseek
    method's responsibilities now) we aren't doing anything hackish or
    unsafe.

    I suspect some (Al) may consider this a suboptimal solution, and I
    agree. However it is a first step -- tightening the locks -- toward a
    better locking scheme, which is hopefully devoid of the BKL.

    The best scores from a slew of dbench runs:

    (2.5.3-pre6 on 2-way Athlon)
    with patch 133.651 165.575 66.9876 37.5297 24.9436
    without patch 132.541 160.774 60.1174 33.2065 22.0126

    Interestingly, the shorter lock times corresponded to an 8.9% reduction
    in scheduling latency (under the above dbench load) with the preemptible
    kernel.

    Robert Love

    diff -urN linux-2.5.3-pre6/Documentation/filesystems/Locking linux/Documentation/filesystems/Locking
    --- linux-2.5.3-pre6/Documentation/filesystems/Locking Mon Jan 28 18:30:27 2002
    +++ linux/Documentation/filesystems/Locking Tue Jan 29 17:07:37 2002
    @@ -219,7 +219,7 @@
    locking rules:
    All except ->poll() may block.
    BKL
    -llseek: yes
    +llseek: yes (see below)
    read: no
    write: no
    readdir: yes (see below)
    @@ -235,6 +235,10 @@
    readv: no
    writev: no

    +->llseek() locking has moved from llseek to the individual llseek
    +implementations. If your fs is not using generic_file_llseek, you
    +need to acquire and release the BKL in your ->llseek().
    +
    ->open() locking is in-transit: big lock partially moved into the methods.
    The only exception is ->open() in the instances of file_operations that never
    end up in ->i_fop/->proc_fops, i.e. ones that belong to character devices
    diff -urN linux-2.5.3-pre6/fs/block_dev.c linux/fs/block_dev.c
    --- linux-2.5.3-pre6/fs/block_dev.c Mon Jan 28 18:30:22 2002
    +++ linux/fs/block_dev.c Tue Jan 29 16:49:52 2002
    @@ -170,6 +170,8 @@
    loff_t size = file->f_dentry->d_inode->i_bdev->bd_inode->i_size;
    loff_t retval;

    + lock_kernel();
    +
    switch (origin) {
    case 2:
    offset += size;
    @@ -186,6 +188,7 @@
    }
    retval = offset;
    }
    + unlock_kernel();
    return retval;
    }

    diff -urN linux-2.5.3-pre6/fs/hfs/file_cap.c linux/fs/hfs/file_cap.c
    --- linux-2.5.3-pre6/fs/hfs/file_cap.c Mon Jan 28 18:30:22 2002
    +++ linux/fs/hfs/file_cap.c Tue Jan 29 16:49:52 2002
    @@ -91,6 +91,8 @@
    {
    long long retval;

    + lock_kernel();
    +
    switch (origin) {
    case 2:
    offset += file->f_dentry->d_inode->i_size;
    @@ -106,6 +108,7 @@
    }
    retval = offset;
    }
    + unlock_kernel();
    return retval;
    }

    diff -urN linux-2.5.3-pre6/fs/hfs/file_hdr.c linux/fs/hfs/file_hdr.c
    --- linux-2.5.3-pre6/fs/hfs/file_hdr.c Mon Jan 28 18:30:22 2002
    +++ linux/fs/hfs/file_hdr.c Tue Jan 29 16:49:52 2002
    @@ -347,6 +347,8 @@
    {
    long long retval;

    + lock_kernel();
    +
    switch (origin) {
    case 2:
    offset += file->f_dentry->d_inode->i_size;
    @@ -362,6 +364,7 @@
    }
    retval = offset;
    }
    + unlock_kernel();
    return retval;
    }

    diff -urN linux-2.5.3-pre6/fs/hpfs/dir.c linux/fs/hpfs/dir.c
    --- linux-2.5.3-pre6/fs/hpfs/dir.c Mon Jan 28 18:30:22 2002
    +++ linux/fs/hpfs/dir.c Tue Jan 29 16:49:52 2002
    @@ -29,6 +29,9 @@
    struct inode *i = filp->f_dentry->d_inode;
    struct hpfs_inode_info *hpfs_inode = hpfs_i(i);
    struct super_block *s = i->i_sb;
    +
    + lock_kernel();
    +
    /*printk("dir lseek\n");*/
    if (new_off == 0 || new_off == 1 || new_off == 11 || new_off == 12 || new_off == 13) goto ok;
    hpfs_lock_inode(i);
    @@ -40,10 +43,12 @@
    }
    hpfs_unlock_inode(i);
    ok:
    + unlock_kernel();
    return filp->f_pos = new_off;
    fail:
    hpfs_unlock_inode(i);
    /*printk("illegal lseek: %016llx\n", new_off);*/
    + unlock_kernel();
    return -ESPIPE;
    }

    diff -urN linux-2.5.3-pre6/fs/proc/generic.c linux/fs/proc/generic.c
    --- linux-2.5.3-pre6/fs/proc/generic.c Mon Jan 28 18:30:22 2002
    +++ linux/fs/proc/generic.c Tue Jan 29 16:49:52 2002
    @@ -16,6 +16,7 @@
    #include <linux/stat.h>
    #define __NO_VERSION__
    #include <linux/module.h>
    +#include <linux/smp_lock.h>
    #include <asm/bitops.h>

    static ssize_t proc_file_read(struct file * file, char * buf,
    @@ -140,22 +141,30 @@
    static loff_t
    proc_file_lseek(struct file * file, loff_t offset, int orig)
    {
    + lock_kernel();
    +
    switch (orig) {
    case 0:
    if (offset < 0)
    - return -EINVAL;
    + goto out;
    file->f_pos = offset;
    + unlock_kernel();
    return(file->f_pos);
    case 1:
    if (offset + file->f_pos < 0)
    - return -EINVAL;
    + goto out;
    file->f_pos += offset;
    + unlock_kernel();
    return(file->f_pos);
    case 2:
    - return(-EINVAL);
    + goto out;
    default:
    - return(-EINVAL);
    + goto out;
    }
    +
    +out:
    + unlock_kernel();
    + return -EINVAL;
    }

    /*
    diff -urN linux-2.5.3-pre6/fs/read_write.c linux/fs/read_write.c
    --- linux-2.5.3-pre6/fs/read_write.c Mon Jan 28 18:30:22 2002
    +++ linux/fs/read_write.c Tue Jan 29 16:49:52 2002
    @@ -29,6 +29,8 @@
    {
    long long retval;

    + down(&file->f_dentry->d_inode->i_sem);
    +
    switch (origin) {
    case 2:
    offset += file->f_dentry->d_inode->i_size;
    @@ -45,6 +47,7 @@
    }
    retval = offset;
    }
    + up(&file->f_dentry->d_inode->i_sem);
    return retval;
    }

    @@ -57,6 +60,8 @@
    {
    long long retval;

    + lock_kernel();
    +
    switch (origin) {
    case 2:
    offset += file->f_dentry->d_inode->i_size;
    @@ -73,6 +78,7 @@
    }
    retval = offset;
    }
    + unlock_kernel();
    return retval;
    }

    @@ -84,9 +90,7 @@
    fn = default_llseek;
    if (file->f_op && file->f_op->llseek)
    fn = file->f_op->llseek;
    - lock_kernel();
    retval = fn(file, offset, origin);
    - unlock_kernel();
    return retval;
    }

    diff -urN linux-2.5.3-pre6/fs/ufs/file.c linux/fs/ufs/file.c
    --- linux-2.5.3-pre6/fs/ufs/file.c Mon Jan 28 18:30:22 2002
    +++ linux/fs/ufs/file.c Tue Jan 29 16:49:52 2002
    @@ -47,6 +47,8 @@
    long long retval;
    struct inode *inode = file->f_dentry->d_inode;

    + lock_kernel();
    +
    switch (origin) {
    case 2:
    offset += inode->i_size;
    @@ -64,6 +66,7 @@
    }
    retval = offset;
    }
    + unlock_kernel();
    return retval;
    }

    -
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