Re: [PATCH 1/3] Add public API for parallel compression method

On Tue, Jan 17, 2023 at 21:58:39 +0800, Jiang Jiacheng wrote: > > > On 2023/1/17 16:44, Claudio Fontana wrote: >> Hi, >> >> On 1/16/23 14:42, Jiang Jiacheng wrote: >>> Add public API VIR_MIGRATE_PARAM_PARALLEL_COMPRESSION, >>> VIR_MIGRATE_PARAM_PARALLEL_ZLIB_LEVEL, VIR_MIGRATE_PARAM_PARALLEL_ZSTD_LEVEL >>> for migration APIs to support set compression method >>> and compress level used during migration. >>> >>> Signed-off-by: Jiang Jiacheng <jiangjiacheng(a)huawei.com&gt; >> >> we don't know what drivers other than QEMU are going to implement in terms of algorithms, >> and we also don't know what new algorithms QEMU will come up with in the future, >> > > Indeed, what you're talking about is better and more scalable. These > patches only adapt to the three parameters of the current version > QEMU，and some commits on the QEMU side may be required to support this > mode. >

>> so I was told when I was working on something similar (but not identical), >> for the "multifd save restore prototype" to try to make it more general. >> >> First of all, maybe we don't need two different _LEVEL parameters, >> just a VIR_MIGRATE_PARAM_PARALLEL_COMPRESSION_LEVEL, which is then mapped in the qemu driver to the specific correct QEMU parameter according to the chosen algo. >> > > Since QEMU sets different parameters for different compression methods, > I've added two corresponding parameters here. If the qemu side does not > change, we can use the same virsh option to input the compression level > and pass the expected QEMU parameters according to the input compression > method on the libvirt side. >

>> Then the VIR_MIGRATE_PARAM_PARALLEL_COMPRESSION could be a freeform string, that is then interpreted by each driver, for example "zlib", or "zstd" in this case. >> So other drivers can pass different strings, and QEMU future new compression algorithms will not need changes to libvirt at all. > > I think what you mean is we can input any string to > VIR_MIGRATE_PARAM_PARALLEL_COMPRESSION and whether it is available is > judged by QEMU or other emulators. > It is supported with these patches, we can use any string for this > parameter, though QEMU only support 'none', 'zlib','zstd' for it, and > other input will return with an error. I think we should just be able to use the existing VIR_MIGRATE_PARAM_COMPRESSION to specify the method. We know whether we're asking for parallel migration from VIR_MIGRATE_PARALLEL flag. We might need to add checks for which compression methods are only allowed with/without VIR_MIGRATE_PARALLEL.

On the other hand, for consistency reasons I think we should add separate VIR_MIGRATE_PARAM_COMPRESSION_ZLIB_LEVEL and VIR_MIGRATE_PARAM_COMPRESSION_ZSTD_LEVEL even though they are the same. The other two compressions methods we currently support (mt and xbzrle) have each their own set of parameters.

Jirka