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[Qemu-devel] Re: [PATCH 2/3 v5] Block live migration
From: |
Jan Kiszka |
Subject: |
[Qemu-devel] Re: [PATCH 2/3 v5] Block live migration |
Date: |
Thu, 26 Nov 2009 08:39:17 +0100 |
User-agent: |
Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv:1.8.1.12) Gecko/20080226 SUSE/2.0.0.12-1.1 Thunderbird/2.0.0.12 Mnenhy/0.7.5.666 |
Liran Schour wrote:
> address@hidden wrote on 25/11/2009 00:55:57:
>
>
>> trying to understand the code and fixing some cosmetic issues around
>> progress reporting, one potentially performance-relevant question popped
> up:
>> address@hidden wrote:
>>> diff --git a/block-migration.c b/block-migration.c
>>> new file mode 100644
>>> index 0000000..4b4eddf
>>> --- /dev/null
>>> +++ b/block-migration.c
>> ...
>>
>>> +static int mig_read_device_bulk(QEMUFile *f, BlkMigDevState *bms)
>>> +{
>>> + int nr_sectors;
>>> + int64_t total_sectors, cur_sector = 0;
>>> + BlockDriverState *bs = bms->bs;
>>> + BlkMigBlock *blk;
>>> +
>>> + blk = qemu_malloc(sizeof(BlkMigBlock));
>>> + blk->buf = qemu_malloc(BLOCK_SIZE);
>>> +
>>> + cur_sector = bms->cur_sector;
>>> + total_sectors = bdrv_getlength(bs) >> SECTOR_BITS;
>> Why re-calculating total_sectors here? Specifically bdrv_getlength() can
>> be a non-trivial I/O operation.
>>
>> And what is the difference to bms->total_sectors which looks a lot
> like...
>> [...]
>>> +
>>> +static void init_blk_migration(QEMUFile *f)
>>> +{
>>> + BlkMigDevState **pbmds, *bmds;
>>> + BlockDriverState *bs;
>>> +
>>> + for (bs = bdrv_first; bs != NULL; bs = bs->next) {
>>> + if(bs->type == BDRV_TYPE_HD) {
>>> + bmds = qemu_mallocz(sizeof(BlkMigDevState));
>>> + bmds->bs = bs;
>>> + bmds->bulk_completed = 0;
>>> + bmds->total_sectors = bdrv_getlength(bs) >> SECTOR_BITS;
>> ...it already contains all the information we need?
>>
>
> You are right no need to figure it out once again. We can use the old
> total_sectors value.
Perfect.
Meanwhile I've quite a few patches here, including that change, will
hopefully manage to send them out today.
Jan
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