| Message ID | 58356E680200007800121299@prv-mh.provo.novell.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
> -----Original Message----- > From: Jan Beulich [mailto:JBeulich@suse.com] > Sent: 23 November 2016 09:25 > To: qemu-devel@nongnu.org > Cc: Anthony Perard <anthony.perard@citrix.com>; Paul Durrant > <Paul.Durrant@citrix.com>; Stefano Stabellini <sstabellini@kernel.org>; xen- > devel <xen-devel@lists.xenproject.org> > Subject: [PATCH 2/3] xen: slightly simplify bufioreq handling > > There's no point setting fields always receiving the same value on each > iteration, as handle_ioreq() doesn't alter them anyway. Set state and > count once ahead of the loop, drop the redundant clearing of > data_is_ptr, and avoid the meaningless setting of df altogether. > > Also avoid doing an unsigned long calculation of size when the field to > be initialized is only 32 bits wide (and the shift value in the range > 0...3). > > Signed-off-by: Jan Beulich <jbeulich@suse.com> Reviewed-by: Paul Durrant <paul.durrant@citrix.com> > > --- a/xen-hvm.c > +++ b/xen-hvm.c > @@ -995,6 +995,8 @@ static int handle_buffered_iopage(XenIOS > } > > memset(&req, 0x00, sizeof(req)); > + req.state = STATE_IOREQ_READY; > + req.count = 1; > > for (;;) { > uint32_t rdptr = buf_page->read_pointer, wrptr; > @@ -1009,15 +1011,11 @@ static int handle_buffered_iopage(XenIOS > break; > } > buf_req = &buf_page->buf_ioreq[rdptr % IOREQ_BUFFER_SLOT_NUM]; > - req.size = 1UL << buf_req->size; > - req.count = 1; > + req.size = 1U << buf_req->size; > req.addr = buf_req->addr; > req.data = buf_req->data; > - req.state = STATE_IOREQ_READY; > req.dir = buf_req->dir; > - req.df = 1; > req.type = buf_req->type; > - req.data_is_ptr = 0; > xen_rmb(); > qw = (req.size == 8); > if (qw) { > @@ -1032,6 +1030,13 @@ static int handle_buffered_iopage(XenIOS > > handle_ioreq(state, &req); > > + /* Only req.data may get updated by handle_ioreq(), albeit even that > + * should not happen as such data would never make it to the guest. > + */ > + assert(req.state == STATE_IOREQ_READY); > + assert(req.count == 1); > + assert(!req.data_is_ptr); > + > atomic_add(&buf_page->read_pointer, qw + 1); > } > > >
On Wed, 23 Nov 2016, Jan Beulich wrote: > There's no point setting fields always receiving the same value on each > iteration, as handle_ioreq() doesn't alter them anyway. Set state and > count once ahead of the loop, drop the redundant clearing of > data_is_ptr, and avoid the meaningless setting of df altogether. Why setting df is meaningless? > Also avoid doing an unsigned long calculation of size when the field to > be initialized is only 32 bits wide (and the shift value in the range > 0...3). > > Signed-off-by: Jan Beulich <jbeulich@suse.com> > > --- a/xen-hvm.c > +++ b/xen-hvm.c > @@ -995,6 +995,8 @@ static int handle_buffered_iopage(XenIOS > } > > memset(&req, 0x00, sizeof(req)); > + req.state = STATE_IOREQ_READY; > + req.count = 1; > > for (;;) { > uint32_t rdptr = buf_page->read_pointer, wrptr; > @@ -1009,15 +1011,11 @@ static int handle_buffered_iopage(XenIOS > break; > } > buf_req = &buf_page->buf_ioreq[rdptr % IOREQ_BUFFER_SLOT_NUM]; > - req.size = 1UL << buf_req->size; > - req.count = 1; > + req.size = 1U << buf_req->size; > req.addr = buf_req->addr; > req.data = buf_req->data; > - req.state = STATE_IOREQ_READY; > req.dir = buf_req->dir; > - req.df = 1; > req.type = buf_req->type; > - req.data_is_ptr = 0; > xen_rmb(); > qw = (req.size == 8); > if (qw) { > @@ -1032,6 +1030,13 @@ static int handle_buffered_iopage(XenIOS > > handle_ioreq(state, &req); > > + /* Only req.data may get updated by handle_ioreq(), albeit even that > + * should not happen as such data would never make it to the guest. > + */ > + assert(req.state == STATE_IOREQ_READY); > + assert(req.count == 1); > + assert(!req.data_is_ptr); > + > atomic_add(&buf_page->read_pointer, qw + 1); > } > > > >
>>> On 23.11.16 at 19:13, <sstabellini@kernel.org> wrote: > On Wed, 23 Nov 2016, Jan Beulich wrote: >> There's no point setting fields always receiving the same value on each >> iteration, as handle_ioreq() doesn't alter them anyway. Set state and >> count once ahead of the loop, drop the redundant clearing of >> data_is_ptr, and avoid the meaningless setting of df altogether. > > Why setting df is meaningless? With count being fixed to one there's no need to update addresses, and hence no use for knowing which direction the updates should go. Jan
--- a/xen-hvm.c +++ b/xen-hvm.c @@ -995,6 +995,8 @@ static int handle_buffered_iopage(XenIOS } memset(&req, 0x00, sizeof(req)); + req.state = STATE_IOREQ_READY; + req.count = 1; for (;;) { uint32_t rdptr = buf_page->read_pointer, wrptr; @@ -1009,15 +1011,11 @@ static int handle_buffered_iopage(XenIOS break; } buf_req = &buf_page->buf_ioreq[rdptr % IOREQ_BUFFER_SLOT_NUM]; - req.size = 1UL << buf_req->size; - req.count = 1; + req.size = 1U << buf_req->size; req.addr = buf_req->addr; req.data = buf_req->data; - req.state = STATE_IOREQ_READY; req.dir = buf_req->dir; - req.df = 1; req.type = buf_req->type; - req.data_is_ptr = 0; xen_rmb(); qw = (req.size == 8); if (qw) { @@ -1032,6 +1030,13 @@ static int handle_buffered_iopage(XenIOS handle_ioreq(state, &req); + /* Only req.data may get updated by handle_ioreq(), albeit even that + * should not happen as such data would never make it to the guest. + */ + assert(req.state == STATE_IOREQ_READY); + assert(req.count == 1); + assert(!req.data_is_ptr); + atomic_add(&buf_page->read_pointer, qw + 1); }
There's no point setting fields always receiving the same value on each iteration, as handle_ioreq() doesn't alter them anyway. Set state and count once ahead of the loop, drop the redundant clearing of data_is_ptr, and avoid the meaningless setting of df altogether. Also avoid doing an unsigned long calculation of size when the field to be initialized is only 32 bits wide (and the shift value in the range 0...3). Signed-off-by: Jan Beulich <jbeulich@suse.com>