| Message ID | 20220622041552.737754-14-viro@zeniv.linux.org.uk (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | [01/44] 9p: handling Rerror without copy_from_iter_full() | expand |
On Wed, 2022-06-22 at 05:15 +0100, Al Viro wrote: > pipe_buffer instances of a pipe are organized as a ring buffer, > with power-of-2 size. Indices are kept *not* reduced modulo ring > size, so the buffer refered to by index N is > pipe->bufs[N & (pipe->ring_size - 1)]. > > Ring size can change over the lifetime of a pipe, but not while > the pipe is locked. So for any iov_iter primitives it's a constant. > Original conversion of pipes to this layout went overboard trying > to microoptimize that - calculating pipe->ring_size - 1, storing > it in a local variable and using through the function. In some > cases it might be warranted, but most of the times it only > obfuscates what's going on in there. > > Introduce a helper (pipe_buf(pipe, N)) that would encapsulate > that and use it in the obvious cases. More will follow... > > Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> > --- > lib/iov_iter.c | 15 +++++++++------ > 1 file changed, 9 insertions(+), 6 deletions(-) > > diff --git a/lib/iov_iter.c b/lib/iov_iter.c > index d00cc8971b5b..08bb393da677 100644 > --- a/lib/iov_iter.c > +++ b/lib/iov_iter.c > @@ -183,13 +183,18 @@ static int copyin(void *to, const void __user *from, size_t n) > return n; > } > > +static inline struct pipe_buffer *pipe_buf(const struct pipe_inode_info *pipe, > + unsigned int slot) > +{ > + return &pipe->bufs[slot & (pipe->ring_size - 1)]; > +} > + > #ifdef PIPE_PARANOIA > static bool sanity(const struct iov_iter *i) > { > struct pipe_inode_info *pipe = i->pipe; > unsigned int p_head = pipe->head; > unsigned int p_tail = pipe->tail; > - unsigned int p_mask = pipe->ring_size - 1; > unsigned int p_occupancy = pipe_occupancy(p_head, p_tail); > unsigned int i_head = i->head; > unsigned int idx; > @@ -201,7 +206,7 @@ static bool sanity(const struct iov_iter *i) > if (unlikely(i_head != p_head - 1)) > goto Bad; // must be at the last buffer... > > - p = &pipe->bufs[i_head & p_mask]; > + p = pipe_buf(pipe, i_head); > if (unlikely(p->offset + p->len != i->iov_offset)) > goto Bad; // ... at the end of segment > } else { > @@ -386,11 +391,10 @@ static inline bool allocated(struct pipe_buffer *buf) > static inline void data_start(const struct iov_iter *i, > unsigned int *iter_headp, size_t *offp) > { > - unsigned int p_mask = i->pipe->ring_size - 1; > unsigned int iter_head = i->head; > size_t off = i->iov_offset; > > - if (off && (!allocated(&i->pipe->bufs[iter_head & p_mask]) || > + if (off && (!allocated(pipe_buf(i->pipe, iter_head)) || > off == PAGE_SIZE)) { > iter_head++; > off = 0; > @@ -1180,10 +1184,9 @@ unsigned long iov_iter_alignment(const struct iov_iter *i) > return iov_iter_alignment_bvec(i); > > if (iov_iter_is_pipe(i)) { > - unsigned int p_mask = i->pipe->ring_size - 1; > size_t size = i->count; > > - if (size && i->iov_offset && allocated(&i->pipe->bufs[i->head & p_mask])) > + if (size && i->iov_offset && allocated(pipe_buf(i->pipe, i->head))) > return size | i->iov_offset; > return size; > } Reviewed-by: Jeff Layton <jlayton@kernel.org>
On Wed, Jun 22, 2022 at 05:15:22AM +0100, Al Viro wrote: > pipe_buffer instances of a pipe are organized as a ring buffer, > with power-of-2 size. Indices are kept *not* reduced modulo ring > size, so the buffer refered to by index N is > pipe->bufs[N & (pipe->ring_size - 1)]. > > Ring size can change over the lifetime of a pipe, but not while > the pipe is locked. So for any iov_iter primitives it's a constant. > Original conversion of pipes to this layout went overboard trying > to microoptimize that - calculating pipe->ring_size - 1, storing > it in a local variable and using through the function. In some > cases it might be warranted, but most of the times it only > obfuscates what's going on in there. > > Introduce a helper (pipe_buf(pipe, N)) that would encapsulate > that and use it in the obvious cases. More will follow... > > Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> > --- Looks good to me, Reviewed-by: Christian Brauner (Microsoft) <brauner@kernel.org>
diff --git a/lib/iov_iter.c b/lib/iov_iter.c index d00cc8971b5b..08bb393da677 100644 --- a/lib/iov_iter.c +++ b/lib/iov_iter.c @@ -183,13 +183,18 @@ static int copyin(void *to, const void __user *from, size_t n) return n; } +static inline struct pipe_buffer *pipe_buf(const struct pipe_inode_info *pipe, + unsigned int slot) +{ + return &pipe->bufs[slot & (pipe->ring_size - 1)]; +} + #ifdef PIPE_PARANOIA static bool sanity(const struct iov_iter *i) { struct pipe_inode_info *pipe = i->pipe; unsigned int p_head = pipe->head; unsigned int p_tail = pipe->tail; - unsigned int p_mask = pipe->ring_size - 1; unsigned int p_occupancy = pipe_occupancy(p_head, p_tail); unsigned int i_head = i->head; unsigned int idx; @@ -201,7 +206,7 @@ static bool sanity(const struct iov_iter *i) if (unlikely(i_head != p_head - 1)) goto Bad; // must be at the last buffer... - p = &pipe->bufs[i_head & p_mask]; + p = pipe_buf(pipe, i_head); if (unlikely(p->offset + p->len != i->iov_offset)) goto Bad; // ... at the end of segment } else { @@ -386,11 +391,10 @@ static inline bool allocated(struct pipe_buffer *buf) static inline void data_start(const struct iov_iter *i, unsigned int *iter_headp, size_t *offp) { - unsigned int p_mask = i->pipe->ring_size - 1; unsigned int iter_head = i->head; size_t off = i->iov_offset; - if (off && (!allocated(&i->pipe->bufs[iter_head & p_mask]) || + if (off && (!allocated(pipe_buf(i->pipe, iter_head)) || off == PAGE_SIZE)) { iter_head++; off = 0; @@ -1180,10 +1184,9 @@ unsigned long iov_iter_alignment(const struct iov_iter *i) return iov_iter_alignment_bvec(i); if (iov_iter_is_pipe(i)) { - unsigned int p_mask = i->pipe->ring_size - 1; size_t size = i->count; - if (size && i->iov_offset && allocated(&i->pipe->bufs[i->head & p_mask])) + if (size && i->iov_offset && allocated(pipe_buf(i->pipe, i->head))) return size | i->iov_offset; return size; }
pipe_buffer instances of a pipe are organized as a ring buffer, with power-of-2 size. Indices are kept *not* reduced modulo ring size, so the buffer refered to by index N is pipe->bufs[N & (pipe->ring_size - 1)]. Ring size can change over the lifetime of a pipe, but not while the pipe is locked. So for any iov_iter primitives it's a constant. Original conversion of pipes to this layout went overboard trying to microoptimize that - calculating pipe->ring_size - 1, storing it in a local variable and using through the function. In some cases it might be warranted, but most of the times it only obfuscates what's going on in there. Introduce a helper (pipe_buf(pipe, N)) that would encapsulate that and use it in the obvious cases. More will follow... Signed-off-by: Al Viro <viro@zeniv.linux.org.uk> --- lib/iov_iter.c | 15 +++++++++------ 1 file changed, 9 insertions(+), 6 deletions(-)