RE: [RFC PATCH 9/9] iov_iter: Add benchmarking kunit tests for UBUF/IOVEC

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



From: David Howells
> Sent: 15 September 2023 11:10
> 
> David Laight <David.Laight@xxxxxxxxxx> wrote:
> 
> > > Add kunit tests to benchmark 256MiB copies to a UBUF iterator and an IOVEC
> > > iterator.  This attaches a userspace VM with a mapped file in it
> > > temporarily to the test thread.
> >
> > Isn't that going to be completely dominated by the cache fills
> > from memory?
> 
> Yes...  but it should be consistent in the amount of time that consumes since
> no device drivers are involved.  I can try adding the same folio to the
> anon_file multiple times - it might work especially if I don't put the pages
> on the LRU (if that's even possible) - but I wanted separate pages for the
> extraction test.

You could also just not do the copy!
Although you need (say) asm volatile("\n",:::"memory") to
stop it all being completely optimised away.
That might show up a difference in the 'out_of_line' test
where 15% on top on the data copies is massive - it may be
that the data cache behaviour is very different for the
two cases.

...
> > Some measurements can be made using readv() and writev()
> > on /dev/zero and /dev/null.
> 
> Forget /dev/null; that doesn't actually engage any iteration code.  The same
> for writing to /dev/zero.  Reading from /dev/zero does its own iteration thing
> rather than using iterate_and_advance(), presumably because it checks for
> signals and resched.

Using /dev/null does exercise the 'copy iov from user' code.
Last time I looked at that the 32bit compat code was faster than
the 64bit code on x86!

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)




[Index of Archives]     [Linux Ext4 Filesystem]     [Union Filesystem]     [Filesystem Testing]     [Ceph Users]     [Ecryptfs]     [NTFS 3]     [AutoFS]     [Kernel Newbies]     [Share Photos]     [Security]     [Netfilter]     [Bugtraq]     [Yosemite News]     [MIPS Linux]     [ARM Linux]     [Linux Security]     [Linux Cachefs]     [Reiser Filesystem]     [Linux RAID]     [NTFS 3]     [Samba]     [Device Mapper]     [CEPH Development]

  Powered by Linux