qemu-devel
[Top][All Lists]
Advanced

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

Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/wr


From: Peter Lieven
Subject: Re: [Qemu-devel] [PATCH 2/4] block: immediately cancel oversized read/write requests
Date: Fri, 12 Sep 2014 13:43:25 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.0

Am 08.09.2014 um 18:29 schrieb Paolo Bonzini:
> Il 08/09/2014 18:18, Peter Lieven ha scritto:
>>>> When copying data, gparted will try using very large I/O sizes.  Of
>>>> course if something breaks it will just use a smaller size, but it would
>>>> make performance worse.
>>>>
>>>> I tried now (with local storage, not virtual---but with such large block
>>>> sizes it's disk bound anyway, one request can take 0.1 seconds to
>>>> execute) and a 2 MB block size is 20% slower than 16 MB block size on
>>>> your usual 3.5" rotational SATA disk.
>>>>
>> can you share with what command exactly you ran these tests?
>>
>> i tried myself and found that without multiwrite_merge i was not able to 
>> create a request bigger than 0xffff sectors from inside linux.
> On a different machine:
>
> $ time dd if=/dev/zero of=test bs=16777216 count=30 oflag=direct
> real  0m13.497s
> user  0m0.001s
> sys   0m0.541s
>
> $ time dd if=/dev/zero of=test2 bs=1048576 count=480 oflag=direct
> real  0m15.835s
> user  0m0.005s
> sys   0m0.770s
>
> The bigger block size is 17% faster; for disk-to-disk copy:
>
> $ time dd if=test of=test3 bs=16777216 count=30 iflag=direct oflag=direct
> real  0m26.075s
> user  0m0.001s
> sys   0m0.678s
>
> $ time dd if=test2 of=test4 bs=1048576 count=480 iflag=direct oflag=direct
> real  0m45.210s
> user  0m0.005s
> sys   0m1.145s
>
> The bigger block size is 73% faster.

I perfectly believe that 16MB blocksize is faster than 2MB. That is true for 
iSCSI as well.

However, I do not see requests of this size coming in via virtio-blk when I ran:

dd if=/dev/zero of=test bs=16777216 count=30 oflag=direct.

As you can see from the multiwrite_merge trace the merging has never been 
stopped because of
the max_transfer_length. The question is, why are the I/O requests not coming 
in as specified?

multiwrite_merge: num_reqs 15 -> 1
iscsi_co_writev: sector_num 0 nb_sectors 15360 bs->bl.max_transfer_length 65535
multiwrite_merge: num_reqs 17 -> 1
iscsi_co_writev: sector_num 15360 nb_sectors 17408 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 32768 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 19 -> 1
iscsi_co_writev: sector_num 44032 nb_sectors 19456 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 2 -> 1
iscsi_co_writev: sector_num 63488 nb_sectors 2048 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 12 -> 1
iscsi_co_writev: sector_num 65536 nb_sectors 12288 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 18 -> 1
iscsi_co_writev: sector_num 77824 nb_sectors 18432 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 2 -> 1
iscsi_co_writev: sector_num 96256 nb_sectors 2048 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 12 -> 1
iscsi_co_writev: sector_num 98304 nb_sectors 12288 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 19 -> 1
iscsi_co_writev: sector_num 110592 nb_sectors 19456 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 1 -> 1
iscsi_co_writev: sector_num 130048 nb_sectors 1024 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 131072 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 19 -> 1
iscsi_co_writev: sector_num 142336 nb_sectors 19456 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 2 -> 1
iscsi_co_writev: sector_num 161792 nb_sectors 2048 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 12 -> 1
iscsi_co_writev: sector_num 163840 nb_sectors 12288 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 19 -> 1
iscsi_co_writev: sector_num 176128 nb_sectors 19456 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 1 -> 1
iscsi_co_writev: sector_num 195584 nb_sectors 1024 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 7 -> 1
iscsi_co_writev: sector_num 196608 nb_sectors 7168 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 18 -> 1
iscsi_co_writev: sector_num 203776 nb_sectors 18432 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 7 -> 1
iscsi_co_writev: sector_num 222208 nb_sectors 7168 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 229376 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 19 -> 1
iscsi_co_writev: sector_num 240640 nb_sectors 19456 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 2 -> 1
iscsi_co_writev: sector_num 260096 nb_sectors 2048 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 262144 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 18 -> 1
iscsi_co_writev: sector_num 273408 nb_sectors 18432 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 3 -> 1
iscsi_co_writev: sector_num 291840 nb_sectors 3072 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 12 -> 1
iscsi_co_writev: sector_num 294912 nb_sectors 12288 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 19 -> 1
iscsi_co_writev: sector_num 307200 nb_sectors 19456 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 1 -> 1
iscsi_co_writev: sector_num 326656 nb_sectors 1024 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 327680 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 19 -> 1
iscsi_co_writev: sector_num 338944 nb_sectors 19456 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 2 -> 1
iscsi_co_writev: sector_num 358400 nb_sectors 2048 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 360448 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 19 -> 1
iscsi_co_writev: sector_num 371712 nb_sectors 19456 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 2 -> 1
iscsi_co_writev: sector_num 391168 nb_sectors 2048 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 393216 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 14 -> 1
iscsi_co_writev: sector_num 404480 nb_sectors 14336 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 7 -> 1
iscsi_co_writev: sector_num 418816 nb_sectors 7168 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 425984 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 20 -> 1
iscsi_co_writev: sector_num 437248 nb_sectors 20480 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 1 -> 1
iscsi_co_writev: sector_num 457728 nb_sectors 1024 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 458752 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 18 -> 1
iscsi_co_writev: sector_num 470016 nb_sectors 18432 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 3 -> 1
iscsi_co_writev: sector_num 488448 nb_sectors 3072 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 491520 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 19 -> 1
iscsi_co_writev: sector_num 502784 nb_sectors 19456 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 2 -> 1
iscsi_co_writev: sector_num 522240 nb_sectors 2048 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 524288 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 18 -> 1
iscsi_co_writev: sector_num 535552 nb_sectors 18432 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 3 -> 1
iscsi_co_writev: sector_num 553984 nb_sectors 3072 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 557056 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 19 -> 1
iscsi_co_writev: sector_num 568320 nb_sectors 19456 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 2 -> 1
iscsi_co_writev: sector_num 587776 nb_sectors 2048 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 589824 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 19 -> 1
iscsi_co_writev: sector_num 601088 nb_sectors 19456 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 2 -> 1
iscsi_co_writev: sector_num 620544 nb_sectors 2048 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 12 -> 1
iscsi_co_writev: sector_num 622592 nb_sectors 12288 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 18 -> 1
iscsi_co_writev: sector_num 634880 nb_sectors 18432 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 2 -> 1
iscsi_co_writev: sector_num 653312 nb_sectors 2048 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 655360 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 19 -> 1
iscsi_co_writev: sector_num 666624 nb_sectors 19456 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 2 -> 1
iscsi_co_writev: sector_num 686080 nb_sectors 2048 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 688128 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 19 -> 1
iscsi_co_writev: sector_num 699392 nb_sectors 19456 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 2 -> 1
iscsi_co_writev: sector_num 718848 nb_sectors 2048 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 9 -> 1
iscsi_co_writev: sector_num 720896 nb_sectors 9216 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 18 -> 1
iscsi_co_writev: sector_num 730112 nb_sectors 18432 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 5 -> 1
iscsi_co_writev: sector_num 748544 nb_sectors 5120 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 12 -> 1
iscsi_co_writev: sector_num 753664 nb_sectors 12288 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 7 -> 1
iscsi_co_writev: sector_num 765952 nb_sectors 7168 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 6 -> 1
iscsi_co_writev: sector_num 773120 nb_sectors 6144 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 7 -> 1
iscsi_co_writev: sector_num 779264 nb_sectors 7168 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 786432 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 14 -> 1
iscsi_co_writev: sector_num 797696 nb_sectors 14336 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 5 -> 1
iscsi_co_writev: sector_num 812032 nb_sectors 5120 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 2 -> 1
iscsi_co_writev: sector_num 817152 nb_sectors 2048 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 8 -> 1
iscsi_co_writev: sector_num 819200 nb_sectors 8192 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 13 -> 1
iscsi_co_writev: sector_num 827392 nb_sectors 13312 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 6 -> 1
iscsi_co_writev: sector_num 840704 nb_sectors 6144 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 5 -> 1
iscsi_co_writev: sector_num 846848 nb_sectors 5120 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 851968 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 14 -> 1
iscsi_co_writev: sector_num 863232 nb_sectors 14336 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 6 -> 1
iscsi_co_writev: sector_num 877568 nb_sectors 6144 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 1 -> 1
iscsi_co_writev: sector_num 883712 nb_sectors 1024 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 884736 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 896000 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 5 -> 1
iscsi_co_writev: sector_num 907264 nb_sectors 5120 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 5 -> 1
iscsi_co_writev: sector_num 912384 nb_sectors 5120 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 11 -> 1
iscsi_co_writev: sector_num 917504 nb_sectors 11264 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 14 -> 1
iscsi_co_writev: sector_num 928768 nb_sectors 14336 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 5 -> 1
iscsi_co_writev: sector_num 943104 nb_sectors 5120 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 2 -> 1
iscsi_co_writev: sector_num 948224 nb_sectors 2048 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 12 -> 1
iscsi_co_writev: sector_num 950272 nb_sectors 12288 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 15 -> 1
iscsi_co_writev: sector_num 962560 nb_sectors 15360 bs->bl.max_transfer_length 
65535
multiwrite_merge: num_reqs 5 -> 1
iscsi_co_writev: sector_num 977920 nb_sectors 5120 bs->bl.max_transfer_length 
65535

Peter

>
> Paolo




reply via email to

[Prev in Thread] Current Thread [Next in Thread]