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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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