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@xxxxxxxxxx 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: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>