Date: Thu, 11 Nov 1999 22:40:08 -0500 From: Simon Shapiro <shimon@simon-shapiro.org> To: "Kenneth D. Merry" <ken@kdm.org> Cc: Randell Jesup <rjesup@wgate.com>, freebsd-arch@freebsd.org Subject: Re: I/O Evaluation Questions (Long but interesting!) Message-ID: <382B8C18.DD84F967@simon-shapiro.org> References: <199911120116.SAA30871@panzer.kdm.org>
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"Kenneth D. Merry" wrote:
>
> [ Simon: the "charset = " (i.e. nothing) line your mail makes my mailer
> barf. You may want to adjust your character set. ]
[ Am using Netscape Messenger. Know not how to do that
(no relevant preference found :-( ]
> Simon Shapiro wrote...
> > Randell Jesup wrote:
> > > Second, could they be (for large IO's) transferring directly
> > > into user memory, bypassing all buffers (I haven't really been following
> > > the discussion; a good trick is to do direct DMA into the destination
> > > buffer - it also allows you to use large commands to the drive (less
> > > command overhead). Saving a memory-to-memory copy counts at those speeds.
> >
> > This happens in FreeBSD on raw I/O. I belive some work was done
> > to do that on block i.o too (something to do with zero copy
> > in vm...
>
> I think you may get this behavior if you turn on the ENABLE_VFS_IOOPT
> option, and then 'sysctl -w vfs.ioopt=1'. It only works for page-sized and
> page-aligned buffers, though. (see sys/ufs/ufs/ufs_readwrite.c)
I'll try that. Thanx.
> I'm not sure how often that kicks in in normal operation. Someone else
> might know.
>
> > > Unlikely, though, and very tricky. (Interesting idea, though -
> > > pseudo-mmap.) They also could set up the DMA, and mark the pages in the
> > > page table so that you'll fault if you try to access them, and then undo
> > > the mark when the IO is done (or as each N pages of the IO is done make
> > > those N pages accessible). There are many cute tricks here...
> > >
> > > What hardware do you have that gives 100MB/s or more???
> >
> > (bragging corner: 167 read, 138 write :-) DPT PM3755U2B with
> > 256MB of ECC cache in a Dell PowerEdge 1300/600.
> > FreeBSD RELENG_3, single CPU running.
>
> How can you get speeds like that with just a 32-bit PCI bus? The specs for
> the PowerEdge 1300 say it has 5 32-bit PCI slots:
These numbers are for block devices. The kernel obviously
caches some of this. I should look next time at emory usage;
The machine has 1GB of memory. The dataset is about 15GB per
array.
I am getting about 120MB/Sec form the PCI
bus. Raw disks perfromance is totally throttled by physics;
We are running at about 200% of Seagate specs.
I am running into some strange situations. Perhaps some
light can be shed;
...
int result;
...
result = tsleep(lock, PRII2O | PCATCH, "i2olck", wait);
switch (result) {
...
}
The above runs correctly.
switch(result = tsleep(lock, PRII2O | PCATCH, "i2olck", wait)) {
This line crashes with an invalid pointer in tsleep().
> http://www.dell.com/us/en/biz/products/spec_wrkgp_1300_servers.htm
>
> Ken
> --
> Kenneth Merry
> ken@kdm.org
--
Sincerely Yours, Shimon@Simon-Shapiro.ORG
404.664.6401
Simon Shapiro
Unwritten code has no bugs and executes at twice the speed of mouth
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