Hello,
I wish to be personally CC'ed the answers/comments posted to the list in
response to this post .
The I/O devices are equipped with dedicated processor to free the main CPU
from doing the low level I/O operations. However, if i am editing and
updating a big size file and i want to save
it afterwards, i notice my PC getting blocked while saving the file which
theoritically should NOT happen as it is up to the I/O device processor and
not the main CPU to save the data into the disk; the main CPU could switch
to another process after giving the high level command -save-to the device
processor; so why the main CPU is blocked while saving such big size files
thanks
_________________________________________________________________
It's fast, it's easy and it's free. Get MSN Messenger today!
http://www.msn.co.uk/messenger
On Mon, Jan 03, 2005 at 12:44:36AM +0000, tony osborne wrote:
> The I/O devices are equipped with dedicated processor to free the main CPU
> from doing the low level I/O operations. However, if i am editing and
^^^^^^^^^^^^^
> updating a big size file and i want to save
> it afterwards, i notice my PC getting blocked while saving the file which
> theoritically should NOT happen as it is up to the I/O device processor and
> not the main CPU to save the data into the disk; the main CPU could switch
> to another process after giving the high level command -save-to the device
^^^^^^^^^^^^^^^^^^
> processor; so why the main CPU is blocked while saving such big size files
--
Martin Waitz
> from doing the low level I/O operations. However, if i am editing and
> updating a big size file and i want to save
> it afterwards, i notice my PC getting blocked while saving the
> file which
> theoritically should NOT happen as it is up to the I/O device
> processor and
What does "PC getting blocked" mean?
DS
sorry for not being clear. i meant no other application running while saving
the data, i.e. CPU idle?
>From: "David Schwartz" <[email protected]>
>Reply-To: [email protected]
>To: <[email protected]>
>CC: <[email protected]>
>Subject: RE: Main CPU- I/O CPU interaction
>Date: Mon, 3 Jan 2005 10:51:43 -0800
>
>
> > from doing the low level I/O operations. However, if i am editing and
> > updating a big size file and i want to save
> > it afterwards, i notice my PC getting blocked while saving the
> > file which
> > theoritically should NOT happen as it is up to the I/O device
> > processor and
>
> What does "PC getting blocked" mean?
>
> DS
>
>
_________________________________________________________________
It's fast, it's easy and it's free. Get MSN Messenger today!
http://www.msn.co.uk/messenger
> sorry for not being clear. i meant no other application running
> while saving
> the data, i.e. CPU idle?
I still have no idea what you're talking about and I don't think anyone
else does either. For example, by CPU being idle, do you mean that it's
doing nothing? If so, how did you establish this? Are you talking about the
output of 'top', for example?
You are going to have to be precise about what your observing. You are
stating your observations in the form of conclusions, and this makes it
impossible for us to tell what you're talking about. It could be that your
misconceptions are coloring your conclusions and others would reach
different conclusions from those same observations.
Example: You are asking, "why does cutting off a frog's legs make it deaf"?
We have no idea what you're talking about. Then you explain your
*observations* which are that if you cut off all of a frog's legs, it no
longer jumps when you yell at it. We then understand that you drew the wrong
conclusion from your observation. But from just the conclusion, there's no
way to tell what you actually are seeing.
"CPU idle" is a conclusion. Something made you think your CPU was idle.
What? Same with your entire post.
DS
On Mon, 03 Jan 2005 00:44:36 GMT, tony osborne said:
> The I/O devices are equipped with dedicated processor to free the main CPU
> from doing the low level I/O operations.
Even a "smart" RAID/SCS/ATA controller is pretty stupid - at best it can be
trusted to find block number N and either read or write it. If you're *really*
lucky, the controller knows about partitions. Any further intelligence is the
realm of IBM-style big iron (where the 'set extent' and 'search key high/low/
equal' CCW commands can offload a significant amount of work). But even there,
the hardware has no filesystem awareness.
> However, if i am editing and
> updating a big size file and i want to save
> it afterwards, i notice my PC getting blocked while saving the file which
> theoritically should NOT happen as it is up to the I/O device processor and
> not the main CPU to save the data into the disk;
What sort of I/O device processor is (a) supported by Linux *and* (b) filesystem
aware? Unless it meets both criteria, the main CPU(s) will still have to do
all the work of block allocation, inode creation, and all the rest of that
stuff.
So what sort of hardware were you thinking of, where the "I/O processor" is
smart enough to handle saving a file (from within an application, no less)
without CPU interference? (and if you're saving the file from within the
application, what API is used to tell the I/O processor whether to use an
"open and fseek to 0" style overwrite, or "rename, creat, write, close, unlink
old" style - all without CPU interference?)
On Llu, 2005-01-03 at 22:27, [email protected] wrote:
> What sort of I/O device processor is (a) supported by Linux *and* (b) filesystem
> aware? Unless it meets both criteria, the main CPU(s) will still have to do
> all the work of block allocation, inode creation, and all the rest of that
> stuff.
NetApp 8)
The offloading file system stuff has been proposed and kicked around and
failed repeatedly in different circles. What has had some success is
offloading layout so that the I/O device thinks in terms of
handle = allocate(blocks, near_this, and_this, ....)
data = read(handle, offset, len)
write(handle, offset, len, data)
free(handle)
type API's, allowing the storage subsystem to do physical
mirror/relocation/HSM in private.
On Sunday 02 January 2005 06:44 pm, tony osborne wrote:
> Hello,
>
> I wish to be personally CC'ed the answers/comments posted to the list in
> response to this post .
>
>
> The I/O devices are equipped with dedicated processor to free the main CPU
> from doing the low level I/O operations. However, if i am editing and
> updating a big size file and i want to save
> it afterwards, i notice my PC getting blocked while saving the file which
> theoritically should NOT happen as it is up to the I/O device processor and
> not the main CPU to save the data into the disk; the main CPU could switch
> to another process after giving the high level command -save-to the device
> processor; so why the main CPU is blocked while saving such big size files
>
> thanks
Check to make sure DMA is on:
hdparm /dev/hda
If not, try turning it on:
hdparm -d 1 /dev/hda
When it's not on, you'll get bad performance (I usually get around 2 MB/s
according to "hdparm -t /dev/hda") and high system CPU usage. Because the
rate is so low, for big files, the high CPU usage starves other processes for
long enough that you notice. With DMA, the transfer will be much faster and
the CPU usage will be minimal.
--
Tom Felker, <[email protected]>
<http://vlevel.sourceforge.net> - Stop fiddling with the volume knob.
If nature has made any one thing less susceptible than all others of exclusive
property, it is the action of the thinking power called an idea.