From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:42790) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZzkJn-00068v-8D for qemu-devel@nongnu.org; Fri, 20 Nov 2015 06:57:32 -0500 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1ZzkJj-0000cW-Sj for qemu-devel@nongnu.org; Fri, 20 Nov 2015 06:57:31 -0500 Received: from [59.151.112.132] (port=4324 helo=heian.cn.fujitsu.com) by eggs.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1ZzkJT-0000Yc-2H for qemu-devel@nongnu.org; Fri, 20 Nov 2015 06:57:27 -0500 References: <1448016301-20944-1-git-send-email-caoj.fnst@cn.fujitsu.com> <20151120124452-mutt-send-email-mst@redhat.com> <564EFE27.5040203@cn.fujitsu.com> <20151120132622-mutt-send-email-mst@redhat.com> From: Cao jin Message-ID: <564F0AC9.3030601@cn.fujitsu.com> Date: Fri, 20 Nov 2015 19:58:01 +0800 MIME-Version: 1.0 In-Reply-To: <20151120132622-mutt-send-email-mst@redhat.com> Content-Type: text/plain; charset="windows-1252"; format=flowed Content-Transfer-Encoding: 7bit Subject: Re: [Qemu-devel] [PATCH] PCI: minor performance optimization List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: "Michael S. Tsirkin" Cc: qemu-devel@nongnu.org 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. > >>>> >>>> Signed-off-by: Cao jin >>>> --- >>>> 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