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Storage And CPU Load: DMA? - Page 2

post #11 of 15
Quote:
Originally Posted by parityboy View Post
But wouldn't it only have to process the permissions once per file? Once it has permission, the file copy should just continue, surely? It can't possibly have to get permission for every block of the file?
I didn't think it would take that much, but you could try moving a file instead of copying it and see if it takes up as much resources.
    
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post #12 of 15
I don't think so.

I needed to do some copying myself so I decided to monitor CPU use.

Going from JFS to JFS (no LVM) locally from the motherboard controller to a Perc5/i RAID5 cp was using between 5-10% of my Atom D525. Seems more reasonable.

May be the high load is due to the file system? Have you tired copying from the motherboard controller to storage elsewhere?
post #13 of 15
Thread Starter 
Girls & guys, many thanks for the responses so far. Just for reference, my RAID 5 array is attached to a Dell SAS 6/iR SAS HBA, created by MD RAID, and formatted for ext4. The RAID 1 array is attached to the onboard Intel H55 SATA controller and is also an MD RAID array, and is also formatted for ext4.

It may well be a filesystem issue. I'm currently copying a 8GB ISO to a USB flash drive, formatted with NTFS. The kio_file process is using 6% CPU time, but the mount.ntfs-3g process (which I assume is an in-kernel process, but maybe not) is taking up 25-30% CPU time. Using cp to perform the file copy results is almost exactly the same numbers, with cp using around 6-7% and mount.ntfs-3g using between 25% and 30%.

OK, I reformatted the USB stick as ext2, and ran the test again. kio_file took ~2% CPU time! Using ext3 as a filesystem, kio_file spiked at 8%, then settled at around 4% average.

I never realised that the filesystems themselves were so CPU-bound. Going by evermooingcow's numbers, it would appear that JFS is one of the best for a high load fileserver, or that ext4 is one of the worst.

I just don't understand what a filesystem could be doing to put so much load on the CPU. Could it be that Canonical have done a poor job of building the Ubuntu kernel? Or is it something inherent in ext4? Either way, it looks like the days of fileservers not being CPU-bound are becoming a thing of the past...
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post #14 of 15
Back when I ran XFS on a Celeron 430 I frequently saw CPU use hitting 100% during copy. I went to a E4500 and my copy speed improved noticeably.

Also I believe ntfs-3g is FUSE.
post #15 of 15
Thread Starter 
I believe you're correct, however ext4 isn't (and therefore has no excuse ). Anyway, now that I know what the culprit is, I can take a view on which filesystem I'll choose to deploy in the future.
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