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Re: [Qemu-devel] [PATCH] PCI: minor performance optimization
From: |
Michael S. Tsirkin |
Subject: |
Re: [Qemu-devel] [PATCH] PCI: minor performance optimization |
Date: |
Fri, 20 Nov 2015 12:45:34 +0200 |
On Fri, Nov 20, 2015 at 06:45:01PM +0800, Cao jin wrote:
> 1. Do param check in pci_add_capability2(), as it is a public API.
Separate patch pls.
> 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?
>
> Signed-off-by: Cao jin <address@hidden>
> ---
> 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