Hi,
I'd like to receive comments/guide-lines about a hack I made to the
2.6.11 kernel to improve DVD-burning speed (using growisofs.)
The basic idea is the 16-pages pipe between mkisofs and growisofs is
too small for DVD burning (typical 4GB of data.)
In the hack, pipe_new will simply check for, if privileges permitted,
the enviroment variable
PIPE_MAX_ORDER to see if a (much) longer pipe is requested.
This hack enable me to burn DVD at 8X (instead of 3X) on my old
P3-450MHz (with growisofs and mkisofs running at SCHED_FIFO.)
--
Linh Dang
--- linux-2.6.11/include/linux/pipe_fs_i.h 2005/03/17 15:39:38
+++ linux-2.6.11-vpipe/include/linux/pipe_fs_i.h 2005/03/23 17:27:12
@@ -21,7 +21,6 @@ struct pipe_buf_operations {
struct pipe_inode_info {
wait_queue_head_t wait;
unsigned int nrbufs, curbuf;
- struct pipe_buffer bufs[PIPE_BUFFERS];
struct page *tmp_page;
unsigned int start;
unsigned int readers;
@@ -31,6 +30,8 @@ struct pipe_inode_info {
unsigned int w_counter;
struct fasync_struct *fasync_readers;
struct fasync_struct *fasync_writers;
+ unsigned max_nr_buffers;
+ struct pipe_buffer bufs[0];
};
/* Differs from PIPE_BUF in that PIPE_SIZE is the length of the actual
--- linux-2.6.11/fs/pipe.c 2005/03/17 15:30:32
+++ linux-2.6.11-vpipe/fs/pipe.c 2005/03/23 17:16:46
@@ -160,7 +160,7 @@ pipe_readv(struct file *filp, const stru
if (!buf->len) {
buf->ops = NULL;
ops->release(info, buf);
- curbuf = (curbuf + 1) & (PIPE_BUFFERS-1);
+ curbuf = (curbuf + 1) & (info->max_nr_buffers - 1);
info->curbuf = curbuf;
info->nrbufs = --bufs;
do_wakeup = 1;
@@ -243,7 +243,7 @@ pipe_writev(struct file *filp, const str
/* We try to merge small writes */
if (info->nrbufs && total_len < PAGE_SIZE) {
- int lastbuf = (info->curbuf + info->nrbufs - 1) & (PIPE_BUFFERS-1);
+ int lastbuf = (info->curbuf + info->nrbufs - 1) & (info->max_nr_buffers-1);
struct pipe_buffer *buf = info->bufs + lastbuf;
struct pipe_buf_operations *ops = buf->ops;
int offset = buf->offset + buf->len;
@@ -270,9 +270,9 @@ pipe_writev(struct file *filp, const str
break;
}
bufs = info->nrbufs;
- if (bufs < PIPE_BUFFERS) {
+ if (bufs < info->max_nr_buffers) {
ssize_t chars;
- int newbuf = (info->curbuf + bufs) & (PIPE_BUFFERS-1);
+ int newbuf = (info->curbuf + bufs) & (info->max_nr_buffers-1);
struct pipe_buffer *buf = info->bufs + newbuf;
struct page *page = info->tmp_page;
int error;
@@ -315,7 +315,7 @@ pipe_writev(struct file *filp, const str
if (!total_len)
break;
}
- if (bufs < PIPE_BUFFERS)
+ if (bufs < info->max_nr_buffers)
continue;
if (filp->f_flags & O_NONBLOCK) {
if (!ret) ret = -EAGAIN;
@@ -382,7 +382,7 @@ pipe_ioctl(struct inode *pino, struct fi
nrbufs = info->nrbufs;
while (--nrbufs >= 0) {
count += info->bufs[buf].len;
- buf = (buf+1) & (PIPE_BUFFERS-1);
+ buf = (buf+1) & (info->max_nr_buffers-1);
}
up(PIPE_SEM(*inode));
return put_user(count, (int __user *)arg);
@@ -412,7 +412,7 @@ pipe_poll(struct file *filp, poll_table
}
if (filp->f_mode & FMODE_WRITE) {
- mask |= (nrbufs < PIPE_BUFFERS) ? POLLOUT | POLLWRNORM : 0;
+ mask |= (nrbufs < info->max_nr_buffers) ? POLLOUT | POLLWRNORM : 0;
if (!PIPE_READERS(*inode))
mask |= POLLERR;
}
@@ -641,7 +641,7 @@ void free_pipe_info(struct inode *inode)
struct pipe_inode_info *info = inode->i_pipe;
inode->i_pipe = NULL;
- for (i = 0; i < PIPE_BUFFERS; i++) {
+ for (i = 0; i < info->max_nr_buffers; i++) {
struct pipe_buffer *buf = info->bufs + i;
if (buf->ops)
buf->ops->release(info, buf);
@@ -653,13 +653,59 @@ void free_pipe_info(struct inode *inode)
struct inode* pipe_new(struct inode* inode)
{
+#define ENV "PIPE_MAX_ORDER="
struct pipe_inode_info *info;
+ struct mm_struct *mm = current ? get_task_mm(current) : NULL;
+
+
+ char* env = NULL;
+ unsigned env_len = 0;
+ unsigned max_nr_buffers = PIPE_BUFFERS;
+
+ if (unlikely(capable(CAP_SYS_RESOURCE))) {
+ if (mm) {
+ env_len = mm->env_end - mm->env_start;
+ env = kmalloc(env_len, GFP_KERNEL);
+ access_process_vm(current, mm->env_start, env, env_len, 0);
+ mmput(mm);
+ }
+
+ if (env) {
+ const char* env_end = env + env_len;
+ char* p = env;
+ char* dummy;
+
+
+ while (p < env_end && strncmp(p, ENV, sizeof(ENV)))
+ p = memscan(p, '\0', env_end - p) + 1;
+
+ if (p < env_end && strncmp(p, ENV, sizeof(ENV)) == 0) {
+ unsigned pipe_nr_buffers_order =
+ simple_strtoul(strchr(p, '='), &dummy, 10);
+
+ if (pipe_nr_buffers_order < 4)
+ pipe_nr_buffers_order = 4;
+
+ if (pipe_nr_buffers_order > 16)
+ pipe_nr_buffers_order = 16;
+
+ max_nr_buffers = 1 << pipe_nr_buffers_order;
+ }
+
+ kfree(env);
+ }
+ }
+
+
+ info = kcalloc(1, sizeof(struct pipe_inode_info) +
+ sizeof(struct pipe_buffer) * max_nr_buffers,
+ GFP_KERNEL);
- info = kmalloc(sizeof(struct pipe_inode_info), GFP_KERNEL);
if (!info)
- goto fail_page;
- memset(info, 0, sizeof(*info));
- inode->i_pipe = info;
+ goto fail_page;
+
+ info->max_nr_buffers = max_nr_buffers;
+ inode->i_pipe = info;
init_waitqueue_head(PIPE_WAIT(*inode));
PIPE_RCOUNTER(*inode) = PIPE_WCOUNTER(*inode) = 1;
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