From mboxrd@z Thu Jan 1 00:00:00 1970 From: Michal Simek Subject: Look for physical address from user space address/fixup - NET_DMA Date: Wed, 08 Jun 2011 16:45:36 +0200 Message-ID: <4DEF8B10.6060904@monstr.eu> Reply-To: monstr@monstr.eu Mime-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit To: Eric Dumazet , netdev@vger.kernel.org, David Miller , Andrew Morton , Ingo Molnar , Thomas Gle Return-path: Sender: owner-linux-mm@kvack.org List-Id: netdev.vger.kernel.org Hi, I do some investigation how to speedup memory operations (memcopy/memset/copy_tofrom_user/etc) by dma to improve ethernet performance (currently for PAGE_SIZE operations). I profiled kernel and copy_tofrom_user is the weakest place for network operations. I have optimize it by loop unrolling which gave me 20% better throughput but still no enough. Then I added hw dma to the design and changed u-boot mem operations (saved me 5s in bootup time - loading 20MB kernel through 100Mbit/s LAN) and also I have add support to Linux memcpy (haven't measured improvement but there is some). For copy_tofrom_user is situation a little bit complicated but I have prototyped it by dma without fixup to see improvement. There could be next 20%. Based on this I have measured spending time on this code and I found that most of the time is spent on looking for physical address from user space address. I need to get physical address because dma requires it. It is around 70% of total time. I use for Microblaze the part of code shown below but it is slow. Do you know how to do it faster? pmd_t *pmdp; pte_t *ptep; pmdp = pmd_offset(pud_offset( pgd_offset(current->mm, address), address), address); preempt_disable(); ptep = pte_offset_map(pmdp, address); if (pte_present(*ptep)) { address = (unsigned long) page_address(pte_page(*ptep)); /* MS: I need add offset in page */ address += address & ~PAGE_MASK; /* MS address is virtual */ address = virt_to_phys(address); } pte_unmap(ptep); preempt_enable(); Currently this is my bottleneck to get better improvement. Not sure if someone has ever tried to replace by dma with fixup support. That's the second thing where I would like to hear your opinion. Would it be possible to simplify it by access user space address and address + PAGE_SIZE? Or any other scheme? There is also one option NET_DMA where I expect that dma will be used instead of mem operations. Is it correct assumption? Because I see that there are no irqs coming from dma. Dma test is working well. Eric, David: How is it supposed to work? Thanks, Michal -- Michal Simek, Ing. (M.Eng) w: www.monstr.eu p: +42-0-721842854 Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/ Microblaze U-BOOT custodian -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: email@kvack.org