On Mon, Nov 04, 2013 at 12:22:26PM -0500, Krishnasamy, Somasundaram wrote:
> Mike,
>
> I was doing some testing with latest dm-cache code (from 'for-next' branch). I
> am having difficulty in making the cache to warm-up. I used the below script
> to read range of blocks repeatedly to get them promoted. I assume after
> reading a block for mq->promote_threshold + 4 times, a block will be
> promoted. But it is not happening. I also tested the same with the
> sequential_threshold set to very high value.
>
> Cache warming-up was relatively easier in the previous dm-cache code. Is this
> something you have seen in your testing?. Is there anything different should I
> do?
I'm also testing with the for-next branch of linux-dm.git and seeing the
same thing as Somu. It's easy to reproduce; reading the same block on the
cached device over and over with dd does not result in that block being
promoted.
I did notice that the "read miss" counter for the cached device increments
each time I execute dd, which I believe means this isn't a buffer cache
issue (I also used dd iflag=direct). The migration_threshold value
shouldn't be an issue for this test, but I set it to a very high value
anyway; didn't make any difference.
Are there any tests in device-mapper-test-suite that you would recommend
for testing whether promotions are occurring as expected?
--Morgan
> Note: /dev/mapper/mydev is the dm-cache target device. I ran the below
> script with "64k 100 100 0" as argument.
> -----------
> #!/bin/bash
>
> if [[ $# -lt 4 ]]
> then
> echo "Usage: $0 <cache_block_size> <nblocks to promote> <nread of a
> block> <start_block>"
> exit 1
> fi
>
> BSSIZE=$1
> ((TOTAL=$2+$4))
> HITCNT=$3
>
> # Read even numbered blocks
> blkcnt=$4
> while [[ blkcnt -lt $TOTAL ]]
> do
> i=0
> echo "Reading block $blkcnt $HITCNT times"
> while [[ $i -lt $HITCNT ]]
> do
> dd if=/dev/mapper/mydev of=/dev/null bs=$BSSIZE skip=$blkcnt
> count=1 conv=notrunc iflag=direct 2> /dev/null
> if [[ $? -ne 0 ]]
> then
> echo "I/O failure. exiting."
> exit 1
> fi
> ((i=i+1))
> done
>
> ((blkcnt=blkcnt+2))
>
> PROMOTED=$(dmsetup status mydev | awk '{print $11}')
> echo "Promoted blocks so far: $PROMOTED"
> done
>
> # Read odd numbered blocks
> ((blkcnt=$4+1))
> while [[ blkcnt -lt $TOTAL ]]
> do
> i=0
> echo "Reading block $blkcnt $HITCNT times"
> while [[ $i -lt $HITCNT ]]
> do
> dd if=/dev/mapper/mydev of=/dev/null bs=$BSSIZE skip=$blkcnt
> count=1 conv=notrunc iflag=direct 2> /dev/null
> if [[ $? -ne 0 ]]
> then
> echo "I/O failure. exiting."
> exit 1
> fi
> ((i=i+1))
> done
>
> ((blkcnt=blkcnt+2))
>
> PROMOTED=$(dmsetup status mydev | awk '{print $11}')
> echo "Promoted blocks so far: $PROMOTED"
> done
> ------------
>
> Regards,
> Somu.
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