I finished my single copy pipe/fifo implementation.
Main changes:
* it's more a rewrite of pipe_read() and pipe_write().
Both functions were a nightmare of nested loops and gotos.
I wrote a test app - with the right timing multiple writers on a fifo
can race and then they busy loop in the current pipe_write() - adding
another set of goto's for single copy is imho a bad idea.
* slightly faster for non-zero copy transfers due to the code
simplification.
* No single copy for exactly 4096 byte writes, only > PIPE_BUF.
Single copy (and thus blocking) such writes could trigger bugs in user
space apps that errorneously assume that a pipe write of PIPE_BUF bytes
after a successful poll(POLLOUT) doesn't block even if O_NONBLOCK is not
set. It's not defined in posix or susv2, but no unix version I tested
blocks in such writes.
* on P II/350 single cpu it's a big win (~+70 % bw_pipe)
* if you run 2 instances on a dual cpu P II/350 it's a big win, but if
you run only one instance, then the bw_pipe processes will jump from one
cpu to the other and it's only a small improvement (~+15%).
I've attached the patch, the test app is at
http://colorfullife.com/~manfred/kiopipe/fail.cpp
Please test it!
-- Manfred
// $Header$ // Kernel Version: // VERSION = 2 // PATCHLEVEL = 4 // SUBLEVEL = 1 // EXTRAVERSION = --- 2.4/fs/pipe.c Thu Nov 16 22:18:26 2000 +++ build-2.4/fs/pipe.c Wed Feb 7 17:17:13 2001 @@ -10,6 +10,8 @@ #include <linux/malloc.h> #include <linux/module.h> #include <linux/init.h> +#include <linux/iobuf.h> +#include <linux/highmem.h> #include <asm/uaccess.h> @@ -35,97 +37,149 @@ down(PIPE_SEM(*inode)); } +struct pipe_pio { + int *pdone; + struct kiobuf iobuf; +}; + +static int +pio_copy_to_user(struct kiobuf* iobuf, int offset, char* ubuf, int chars) +{ + int page_nr; + offset += iobuf->offset; + page_nr = offset/PAGE_SIZE; + offset %= PAGE_SIZE; + while(chars) { + int pcount = PAGE_SIZE-offset; + void *kaddr; + if (pcount > chars) + pcount = chars; + kaddr = kmap(iobuf->maplist[page_nr]); + if (copy_to_user(ubuf, kaddr+offset, pcount)) + return 1; + kunmap(iobuf->maplist[page_nr]); + chars -= pcount; + ubuf += pcount; + offset = 0; + page_nr++; + } + return 0; +} + static ssize_t pipe_read(struct file *filp, char *buf, size_t count, loff_t *ppos) { struct inode *inode = filp->f_dentry->d_inode; - ssize_t size, read, ret; + ssize_t read, ret; - /* Seeks are not allowed on pipes. */ - ret = -ESPIPE; - read = 0; + /* pread is not allowed on pipes. */ if (ppos != &filp->f_pos) - goto out_nolock; + return -ESPIPE; /* Always return 0 on null read. */ - ret = 0; if (count == 0) - goto out_nolock; + return 0; - /* Get the pipe semaphore */ - ret = -ERESTARTSYS; - if (down_interruptible(PIPE_SEM(*inode))) - goto out_nolock; + down(PIPE_SEM(*inode)); - if (PIPE_EMPTY(*inode)) { -do_more_read: + read = 0; + for (;;) { + /* read what data is available */ + int chars = PIPE_LEN(*inode); + if (chars) { + char *pipebuf = PIPE_BASE(*inode); + int offset = PIPE_START(*inode); + + if (chars > count) + chars = count; + ret = -EFAULT; + if(PIPE_IS_PIO(*inode)) { + struct pipe_pio* pio = ((struct pipe_pio*)pipebuf); + if(pio_copy_to_user(&pio->iobuf, offset, buf, chars)) + goto out; + + PIPE_LEN(*inode) -= chars; + if(!PIPE_LEN(*inode)) { + unmap_kiobuf(&pio->iobuf); + *pio->pdone = 1; + PIPE_IS_PIO(*inode) = 0; + PIPE_START(*inode) = 0; + } else { + PIPE_START(*inode) += chars; + } + } else { + if (chars > PIPE_SIZE-offset) + chars = PIPE_SIZE-offset; + if (copy_to_user(buf, pipebuf+offset, chars)) + goto out; + PIPE_LEN(*inode) -= chars; + if (!PIPE_LEN(*inode)) { + /* Cache behaviour optimization */ + PIPE_START(*inode) = 0; + } else { + PIPE_START(*inode) += chars; + PIPE_START(*inode) &= (PIPE_SIZE - 1); + } + } + read += chars; + count -= chars; + buf += chars; + } ret = 0; + if (!count) + goto out; + + /* Rare special case: + * The pipe buffer was really circular, + * the wrapped bytes must be read before sleeping. + */ + if (PIPE_LEN(*inode)) + continue; + + /* Never sleep if no process has the pipe open + * for writing */ if (!PIPE_WRITERS(*inode)) goto out; + /* Never sleep if O_NONBLOCK is set */ ret = -EAGAIN; if (filp->f_flags & O_NONBLOCK) goto out; - for (;;) { - PIPE_WAITING_READERS(*inode)++; - pipe_wait(inode); - PIPE_WAITING_READERS(*inode)--; - ret = -ERESTARTSYS; - if (signal_pending(current)) - goto out; + /* optimization: + * pipe_read() should return even if only a single byte + * was read. (Posix Std. 6.4.1.2) + * But if another process is sleeping in pipe_write() + * then we wait for that data - it's invisible for user + * space programs. + */ + if (PIPE_MORE_DATA_WAITING(*inode)) { + /* + * We know that we are going to sleep: signal + * writers synchronously that there is more + * room. + */ + wake_up_interruptible_sync(PIPE_WAIT(*inode)); + } else if (read) { + /* We know that there are no writers, no need + * for wake up. + */ ret = 0; - if (!PIPE_EMPTY(*inode)) - break; - if (!PIPE_WRITERS(*inode)) - goto out; + goto out; } - } - /* Read what data is available. */ - ret = -EFAULT; - while (count > 0 && (size = PIPE_LEN(*inode))) { - char *pipebuf = PIPE_BASE(*inode) + PIPE_START(*inode); - ssize_t chars = PIPE_MAX_RCHUNK(*inode); - - if (chars > count) - chars = count; - if (chars > size) - chars = size; - - if (copy_to_user(buf, pipebuf, chars)) + pipe_wait(inode); + ret = -ERESTARTSYS; + if (signal_pending(current)) goto out; - - read += chars; - PIPE_START(*inode) += chars; - PIPE_START(*inode) &= (PIPE_SIZE - 1); - PIPE_LEN(*inode) -= chars; - count -= chars; - buf += chars; } - /* Cache behaviour optimization */ - if (!PIPE_LEN(*inode)) - PIPE_START(*inode) = 0; - - if (count && PIPE_WAITING_WRITERS(*inode) && !(filp->f_flags & O_NONBLOCK)) { - /* - * We know that we are going to sleep: signal - * writers synchronously that there is more - * room. - */ - wake_up_interruptible_sync(PIPE_WAIT(*inode)); - if (!PIPE_EMPTY(*inode)) - BUG(); - goto do_more_read; - } +out: /* Signal writers asynchronously that there is more room. */ - wake_up_interruptible(PIPE_WAIT(*inode)); + if (read && !PIPE_IS_PIO(*inode)) + wake_up_interruptible(PIPE_WAIT(*inode)); - ret = read; -out: up(PIPE_SEM(*inode)); -out_nolock: if (read) ret = read; return ret; @@ -136,113 +190,143 @@ { struct inode *inode = filp->f_dentry->d_inode; ssize_t free, written, ret; + int pio_done, do_wakeup; - /* Seeks are not allowed on pipes. */ - ret = -ESPIPE; - written = 0; + /* pwrite is not allowed on pipes. */ if (ppos != &filp->f_pos) - goto out_nolock; + return -ESPIPE; /* Null write succeeds. */ - ret = 0; if (count == 0) - goto out_nolock; - - ret = -ERESTARTSYS; - if (down_interruptible(PIPE_SEM(*inode))) - goto out_nolock; + return 0; - /* No readers yields SIGPIPE. */ - if (!PIPE_READERS(*inode)) - goto sigpipe; + down(PIPE_SEM(*inode)); /* If count <= PIPE_BUF, we have to make it atomic. */ free = (count <= PIPE_BUF ? count : 1); - /* Wait, or check for, available space. */ - if (filp->f_flags & O_NONBLOCK) { - ret = -EAGAIN; - if (PIPE_FREE(*inode) < free) + written = 0; + pio_done = 1; + do_wakeup = 0; + for(;;) { + /* No readers yields SIGPIPE. */ + ret = -EPIPE; + if (!PIPE_READERS(*inode)) goto out; - } else { - while (PIPE_FREE(*inode) < free) { - PIPE_WAITING_WRITERS(*inode)++; - pipe_wait(inode); - PIPE_WAITING_WRITERS(*inode)--; - ret = -ERESTARTSYS; - if (signal_pending(current)) - goto out; - if (!PIPE_READERS(*inode)) - goto sigpipe; - } - } - - /* Copy into available space. */ - ret = -EFAULT; - while (count > 0) { - int space; - char *pipebuf = PIPE_BASE(*inode) + PIPE_END(*inode); - ssize_t chars = PIPE_MAX_WCHUNK(*inode); - - if ((space = PIPE_FREE(*inode)) != 0) { - if (chars > count) - chars = count; - if (chars > space) - chars = space; - - if (copy_from_user(pipebuf, buf, chars)) - goto out; - - written += chars; - PIPE_LEN(*inode) += chars; - count -= chars; - buf += chars; - space = PIPE_FREE(*inode); - continue; + if(!PIPE_IS_PIO(*inode)) { + int chars; + /* Copy into available space. */ + chars = PIPE_FREE(*inode); + + /* + * Try zero-copy: + * - only possible if the normal pipe buffer + * is empty + * - only possible if we can block: + * a) O_NONBLOCK not set + * and + * b) request for more than PIPE_BUF bytes. + * No Unix version blocks in pipe write for + * <= PIPE_BUF bytes after poll() returned POLLOUT. + */ + ret = -EFAULT; + if (count > PIPE_BUF && chars == PIPE_SIZE && + (!(filp->f_flags & O_NONBLOCK))) { + struct pipe_pio* pio = (struct pipe_pio*)PIPE_BASE(*inode); + chars = KIO_MAX_ATOMIC_BYTES; + if (chars > count) + chars = count; + kiobuf_init(&pio->iobuf); + if(map_user_kiobuf(READ, &pio->iobuf, (unsigned long)buf, chars)) + goto out; + PIPE_IS_PIO(*inode) = 1; + pio_done = 0; + pio->pdone = &pio_done; + + written += chars; + PIPE_LEN(*inode) += chars; + count -= chars; + buf += chars; + do_wakeup = 1; + } else if (chars >= free) { + int offset; +next_chunk: + offset = PIPE_END(*inode); + + if (chars > count) + chars = count; + if (chars > PIPE_SIZE-offset) + chars = PIPE_SIZE-offset; + if (copy_from_user(PIPE_BASE(*inode)+offset, buf, chars)) + goto out; + + written += chars; + PIPE_LEN(*inode) += chars; + count -= chars; + buf += chars; + do_wakeup = 1; + + if(!count) + break; /* DONE! */ + + /* special case: pipe buffer wrapped */ + if(PIPE_LEN(*inode) != PIPE_SIZE) { + chars = PIPE_FREE(*inode); + goto next_chunk; + } + } } - ret = written; + ret = -EAGAIN; if (filp->f_flags & O_NONBLOCK) break; - do { + /* Do not wakeup unless data was written, otherwise + * multiple writers can cause a wakeup storm + */ + if(do_wakeup) { /* * Synchronous wake-up: it knows that this process * is going to give up this CPU, so it doesnt have * to do idle reschedules. */ wake_up_interruptible_sync(PIPE_WAIT(*inode)); - PIPE_WAITING_WRITERS(*inode)++; - pipe_wait(inode); - PIPE_WAITING_WRITERS(*inode)--; - if (signal_pending(current)) - goto out; - if (!PIPE_READERS(*inode)) - goto sigpipe; - } while (!PIPE_FREE(*inode)); - ret = -EFAULT; + do_wakeup = 0; + } + if (count) + PIPE_MORE_DATA_WAITING(*inode)++; + pipe_wait(inode); + if (count) + PIPE_MORE_DATA_WAITING(*inode)--; + if (!count && pio_done) + break; /* DONE */ + ret = -ERESTARTSYS; + if (signal_pending(current)) + goto out; } - - /* Signal readers asynchronously that there is more data. */ - wake_up_interruptible(PIPE_WAIT(*inode)); - - inode->i_ctime = inode->i_mtime = CURRENT_TIME; - mark_inode_dirty(inode); - out: - up(PIPE_SEM(*inode)); -out_nolock: - if (written) - ret = written; - return ret; + if(!pio_done) { + struct pipe_pio* pio = (struct pipe_pio*)PIPE_BASE(*inode); + PIPE_IS_PIO(*inode) = 0; + written -= PIPE_LEN(*inode); + PIPE_LEN(*inode) = 0; + unmap_kiobuf(&pio->iobuf); + wake_up_interruptible(PIPE_WAIT(*inode)); + } + if (written) { + inode->i_ctime = inode->i_mtime = CURRENT_TIME; + mark_inode_dirty(inode); -sigpipe: - if (written) - goto out; + ret = written; + } up(PIPE_SEM(*inode)); - send_sig(SIGPIPE, current, 0); - return -EPIPE; + /* Signal readers asynchronously that there is more data. */ + if(do_wakeup) + wake_up_interruptible(PIPE_WAIT(*inode)); + if (ret == -EPIPE) + send_sig(SIGPIPE, current, 0); + return ret; } static loff_t @@ -453,9 +537,10 @@ init_waitqueue_head(PIPE_WAIT(*inode)); PIPE_BASE(*inode) = (char*) page; + PIPE_IS_PIO(*inode) = 0; PIPE_START(*inode) = PIPE_LEN(*inode) = 0; PIPE_READERS(*inode) = PIPE_WRITERS(*inode) = 0; - PIPE_WAITING_READERS(*inode) = PIPE_WAITING_WRITERS(*inode) = 0; + PIPE_MORE_DATA_WAITING(*inode) = 0; PIPE_RCOUNTER(*inode) = PIPE_WCOUNTER(*inode) = 1; return inode; --- 2.4/include/linux/pipe_fs_i.h Mon May 8 20:17:47 2000 +++ build-2.4/include/linux/pipe_fs_i.h Tue Feb 6 13:29:48 2001 @@ -5,11 +5,11 @@ struct pipe_inode_info { wait_queue_head_t wait; char *base; + unsigned int is_pio; unsigned int start; unsigned int readers; unsigned int writers; - unsigned int waiting_readers; - unsigned int waiting_writers; + unsigned int more_data; unsigned int r_counter; unsigned int w_counter; }; @@ -21,12 +21,12 @@ #define PIPE_SEM(inode) (&(inode).i_sem) #define PIPE_WAIT(inode) (&(inode).i_pipe->wait) #define PIPE_BASE(inode) ((inode).i_pipe->base) +#define PIPE_IS_PIO(inode) ((inode).i_pipe->is_pio) #define PIPE_START(inode) ((inode).i_pipe->start) #define PIPE_LEN(inode) ((inode).i_size) #define PIPE_READERS(inode) ((inode).i_pipe->readers) #define PIPE_WRITERS(inode) ((inode).i_pipe->writers) -#define PIPE_WAITING_READERS(inode) ((inode).i_pipe->waiting_readers) -#define PIPE_WAITING_WRITERS(inode) ((inode).i_pipe->waiting_writers) +#define PIPE_MORE_DATA_WAITING(inode) ((inode).i_pipe->more_data) #define PIPE_RCOUNTER(inode) ((inode).i_pipe->r_counter) #define PIPE_WCOUNTER(inode) ((inode).i_pipe->w_counter) @@ -34,8 +34,6 @@ #define PIPE_FULL(inode) (PIPE_LEN(inode) == PIPE_SIZE) #define PIPE_FREE(inode) (PIPE_SIZE - PIPE_LEN(inode)) #define PIPE_END(inode) ((PIPE_START(inode) + PIPE_LEN(inode)) & (PIPE_SIZE-1)) -#define PIPE_MAX_RCHUNK(inode) (PIPE_SIZE - PIPE_START(inode)) -#define PIPE_MAX_WCHUNK(inode) (PIPE_SIZE - PIPE_END(inode)) /* Drop the inode semaphore and wait for a pipe event, atomically */ void pipe_wait(struct inode * inode);
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This archive was generated by hypermail 2b29 : Wed Feb 07 2001 - 21:00:28 EST