> -----Original Message----- > From: Daniel P. Berrangé <berra...@redhat.com> > Sent: Thursday, October 19, 2023 11:32 PM > To: Peter Xu <pet...@redhat.com> > Cc: Juan Quintela <quint...@redhat.com>; Liu, Yuan1 > <yuan1....@intel.com>; faro...@suse.de; leob...@redhat.com; qemu- > de...@nongnu.org; Zou, Nanhai <nanhai....@intel.com> > Subject: Re: [PATCH 0/5] Live Migration Acceleration with IAA Compression > > On Thu, Oct 19, 2023 at 11:23:31AM -0400, Peter Xu wrote: > > On Thu, Oct 19, 2023 at 03:52:14PM +0100, Daniel P. Berrangé wrote: > > > On Thu, Oct 19, 2023 at 01:40:23PM +0200, Juan Quintela wrote: > > > > Yuan Liu <yuan1....@intel.com> wrote: > > > > > Hi, > > > > > > > > > > I am writing to submit a code change aimed at enhancing live > > > > > migration acceleration by leveraging the compression capability > > > > > of the Intel In-Memory Analytics Accelerator (IAA). > > > > > > > > > > Enabling compression functionality during the live migration > > > > > process can enhance performance, thereby reducing downtime and > > > > > network bandwidth requirements. However, this improvement comes > > > > > at the cost of additional CPU resources, posing a challenge for > > > > > cloud service providers in terms of resource allocation. To > > > > > address this challenge, I have focused on offloading the compression > overhead to the IAA hardware, resulting in performance gains. > > > > > > > > > > The implementation of the IAA (de)compression code is based on > > > > > Intel Query Processing Library (QPL), an open-source software > > > > > project designed for IAA high-level software programming. > > > > > > > > > > Best regards, > > > > > Yuan Liu > > > > > > > > After reviewing the patches: > > > > > > > > - why are you doing this on top of old compression code, that is > > > > obsolete, deprecated and buggy Some users have not enabled the multifd feature yet, but they will decide whether to enable the compression feature based on the load situation. So I'm wondering if, without multifd, the compression functionality will no longer be available?
> > > > - why are you not doing it on top of multifd. I plan to submit the support for multifd independently because the multifd compression and legacy compression code are separate. I looked at the code of multifd about compression. Currently, it uses the CPU synchronous compression mode. Since it is best to use the asynchronous processing method of the hardware accelerator, I would like to get suggestions on the asynchronous implementation. 1. Dirty page scanning and compression pipeline processing, the main thread of live migration submits compression tasks to the hardware, and multifd threads only handle the transmission of compressed pages. 2. Data sending and compression pipeline processing, the Multifd threads submit compression tasks to the hardware and then transmit the compressed data. (A multifd thread job may need to transmit compressed data multiple times.) > > > > You just need to add another compression method on top of multifd. > > > > See how it was done for zstd: Yes, I will refer to zstd to implement multifd compression with IAA > > > I'm not sure that is ideal approach. IIUC, the IAA/QPL library is > > > not defining a new compression format. Rather it is providing a > > > hardware accelerator for 'deflate' format, as can be made compatible > > > with zlib: > > > > > > > > > https://intel.github.io/qpl/documentation/dev_guide_docs/c_use_cases > > > /deflate/c_deflate_zlib_gzip.html#zlib-and-gzip-compatibility-refere > > > nce-link > > > > > > With multifd we already have a 'zlib' compression format, and so > > > this IAA/QPL logic would effectively just be a providing a second > > > implementation of zlib. > > > > > > Given the use of a standard format, I would expect to be able to use > > > software zlib on the src, mixed with IAA/QPL zlib on the target, or > > > vica-verca. > > > > > > IOW, rather than defining a new compression format for this, I think > > > we could look at a new migration parameter for > > > > > > "compression-accelerator": ["auto", "none", "qpl"] > > > > > > with 'auto' the default, such that we can automatically enable > > > IAA/QPL when 'zlib' format is requested, if running on a suitable > > > host. > > > > I was also curious about the format of compression comparing to > > software ones when reading. > > > > Would there be a use case that one would prefer soft compression even > > if hardware accelerator existed, no matter on src/dst? > > > > I'm wondering whether we can avoid that one more parameter but always > > use hardware accelerations as long as possible. I want to add a new compression format(QPL or IAA-Deflate) here. The reasons are as follows: 1. The QPL library already supports both software and hardware paths for compression. The software path uses a fast Deflate compression algorithm, while the hardware path uses IAA. 2. QPL's software and hardware paths are based on the Deflate algorithm, but there is a limitation: the history buffer only supports 4K. The default history buffer for zlib is 32K, which means that IAA cannot decompress zlib-compressed data. However, zlib can decompress IAA-compressed data. 3. For zlib and zstd, Intel QuickAssist Technology can accelerate both of them. > Yeah, I did wonder about whether we could avoid a parameter, but then I'm > thinking it is good to have an escape hatch if we were to find any flaws in > the > QPL library's impl of deflate() that caused interop problems. > > With regards, > Daniel > -- > |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| > |: https://libvirt.org -o- https://fstop138.berrange.com :| > |: https://entangle-photo.org -o- > https://www.instagram.com/dberrange :|
