On Fri, Nov 20, 2015 at 07:58:01PM +0800, Cao jin wrote:
>
>
> On 11/20/2015 07:26 PM, Michael S. Tsirkin wrote:
> >On Fri, Nov 20, 2015 at 07:04:07PM +0800, Cao jin wrote:
> >>
> >>
> >>On 11/20/2015 06:45 PM, Michael S. Tsirkin wrote:
> >>>On Fri, Nov 20, 2015 at 06:45:01PM +0800, Cao jin wrote:
> >>>
> >>>>2. As spec says, each capability must be DWORD aligned, so an
> >>>>optimization can
> >>>> be done via Loop Unrolling.
> >>>
> >>>Why do we want to optimize it?
> >>>
> >>
> >>For tiny performance improvement via less loop. take pcie express
> >>capability(60 bytes at most) for example, it may loop 60 times, now we just
> >>need 15 times, a quarter of before.
> >
> >But who cares? This is not a data path operation.
>
> It is tiny thing I found when browsing code. When found there are several
> places looks like this, I think maybe it does good to qemu to do this and
> CCed to you because it don`t look like a simple trivial patch.
>
> So, hey Michael, if you don`t like this kind of optimization, that`t ok,
> forget it. But I think it make me little confused when determine which kind
> of patch should be CCed to you.
Optimization patches should normally include performance numbers
if they are to be merged.
Try to come up with a benchmark and you will realize that the speed of
this function has no effect under even half way realistic conditions.
> >
> >>>>
> >>>>Signed-off-by: Cao jin <caoj.f...@cn.fujitsu.com>
> >>>>---
> >>>> hw/pci/pci.c | 12 ++++++++----
> >>>> 1 file changed, 8 insertions(+), 4 deletions(-)
> >>>>
> >>>>diff --git a/hw/pci/pci.c b/hw/pci/pci.c
> >>>>index 168b9cc..1e99603 100644
> >>>>--- a/hw/pci/pci.c
> >>>>+++ b/hw/pci/pci.c
> >>>>@@ -1924,13 +1924,15 @@ PCIDevice *pci_create_simple(PCIBus *bus, int
> >>>>devfn, const char *name)
> >>>> static uint8_t pci_find_space(PCIDevice *pdev, uint8_t size)
> >>>> {
> >>>> int offset = PCI_CONFIG_HEADER_SIZE;
> >>>>- int i;
> >>>>- for (i = PCI_CONFIG_HEADER_SIZE; i < PCI_CONFIG_SPACE_SIZE; ++i) {
> >>>>+ int i = PCI_CONFIG_HEADER_SIZE;;
> >>>>+
> >>>>+ for (; i < PCI_CONFIG_SPACE_SIZE; i = i + 4) {
> >>>> if (pdev->used[i])
> >>>>- offset = i + 1;
> >>>>- else if (i - offset + 1 == size)
> >>>>+ offset = i + 4;
> >>>>+ else if (i - offset >= size)
> >>>> return offset;
> >>>> }
> >>>>+
> >>>> return 0;
> >>>> }
> >>>>
> >>>>@@ -2144,6 +2146,8 @@ int pci_add_capability2(PCIDevice *pdev, uint8_t
> >>>>cap_id,
> >>>> uint8_t *config;
> >>>> int i, overlapping_cap;
> >>>>
> >>>>+ assert(size > 0);
> >>>>+
> >>>> if (!offset) {
> >>>> offset = pci_find_space(pdev, size);
> >>>> if (!offset) {
> >>>>--
> >>>>2.1.0
> >>>.
> >>>
> >>
> >>--
> >>Yours Sincerely,
> >>
> >>Cao Jin
> >.
> >
>
> --
> Yours Sincerely,
>
> Cao Jin
