From: "Dr. David Alan Gilbert" <dgilbert@redhat.com> To: Peter Xu <peterx@redhat.com>, quintela@redhat.com Cc: kvm@vger.kernel.org, mst@redhat.com, mtosatti@redhat.com, Xiao Guangrong <xiaoguangrong@tencent.com>, qemu-devel@nongnu.org, wei.w.wang@intel.com, guangrong.xiao@gmail.com, jiang.biao2@zte.com.cn, pbonzini@redhat.com Subject: Re: [PATCH] migration: fix saving normal page even if it's been compressed Date: Wed, 2 May 2018 16:30:39 +0100 [thread overview] Message-ID: <20180502153039.GF2679@work-vm> (raw) In-Reply-To: <20180502024653.GB25938@xz-mi> * Peter Xu (peterx@redhat.com) wrote: > On Sat, Apr 28, 2018 at 04:10:45PM +0800, guangrong.xiao@gmail.com wrote: > > From: Xiao Guangrong <xiaoguangrong@tencent.com> > > > > Fix the bug introduced by da3f56cb2e767016 (migration: remove > > ram_save_compressed_page()), It should be 'return' rather than > > 'res' > > > > Sorry for this stupid mistake :( > > > > Signed-off-by: Xiao Guangrong <xiaoguangrong@tencent.com> > > Reviewed-by: Peter Xu <peterx@redhat.com> > > So is that only a performance degradation without this fix (since > AFAIU the compressing pages will be sent twice)? Thanks, It might be a bit more messy than that; because I think the 'compress_page_with_multi_thread' hands it to a compression thread to compress and write, but I don't think it waits for it. So I think you'll end up with this being written at the same time as the uncompressed data is written - I'm not sure what the other end receives. (Which makes me realise I don't think I understand how the compression threads are safe with their writing data out). Anyway, I think we should get this one in quickly. Dave > > --- > > migration/ram.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/migration/ram.c b/migration/ram.c > > index 01cc815410..699546cc43 100644 > > --- a/migration/ram.c > > +++ b/migration/ram.c > > @@ -1490,7 +1490,7 @@ static int ram_save_target_page(RAMState *rs, PageSearchStatus *pss, > > * CPU resource. > > */ > > if (block == rs->last_sent_block && save_page_use_compression(rs)) { > > - res = compress_page_with_multi_thread(rs, block, offset); > > + return compress_page_with_multi_thread(rs, block, offset); > > } > > > > return ram_save_page(rs, pss, last_stage); > > -- > > 2.14.3 > > > > -- > Peter Xu -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
WARNING: multiple messages have this Message-ID (diff)
From: "Dr. David Alan Gilbert" <dgilbert@redhat.com> To: Peter Xu <peterx@redhat.com>, quintela@redhat.com Cc: guangrong.xiao@gmail.com, pbonzini@redhat.com, mst@redhat.com, mtosatti@redhat.com, qemu-devel@nongnu.org, kvm@vger.kernel.org, jiang.biao2@zte.com.cn, wei.w.wang@intel.com, Xiao Guangrong <xiaoguangrong@tencent.com> Subject: Re: [Qemu-devel] [PATCH] migration: fix saving normal page even if it's been compressed Date: Wed, 2 May 2018 16:30:39 +0100 [thread overview] Message-ID: <20180502153039.GF2679@work-vm> (raw) In-Reply-To: <20180502024653.GB25938@xz-mi> * Peter Xu (peterx@redhat.com) wrote: > On Sat, Apr 28, 2018 at 04:10:45PM +0800, guangrong.xiao@gmail.com wrote: > > From: Xiao Guangrong <xiaoguangrong@tencent.com> > > > > Fix the bug introduced by da3f56cb2e767016 (migration: remove > > ram_save_compressed_page()), It should be 'return' rather than > > 'res' > > > > Sorry for this stupid mistake :( > > > > Signed-off-by: Xiao Guangrong <xiaoguangrong@tencent.com> > > Reviewed-by: Peter Xu <peterx@redhat.com> > > So is that only a performance degradation without this fix (since > AFAIU the compressing pages will be sent twice)? Thanks, It might be a bit more messy than that; because I think the 'compress_page_with_multi_thread' hands it to a compression thread to compress and write, but I don't think it waits for it. So I think you'll end up with this being written at the same time as the uncompressed data is written - I'm not sure what the other end receives. (Which makes me realise I don't think I understand how the compression threads are safe with their writing data out). Anyway, I think we should get this one in quickly. Dave > > --- > > migration/ram.c | 2 +- > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > diff --git a/migration/ram.c b/migration/ram.c > > index 01cc815410..699546cc43 100644 > > --- a/migration/ram.c > > +++ b/migration/ram.c > > @@ -1490,7 +1490,7 @@ static int ram_save_target_page(RAMState *rs, PageSearchStatus *pss, > > * CPU resource. > > */ > > if (block == rs->last_sent_block && save_page_use_compression(rs)) { > > - res = compress_page_with_multi_thread(rs, block, offset); > > + return compress_page_with_multi_thread(rs, block, offset); > > } > > > > return ram_save_page(rs, pss, last_stage); > > -- > > 2.14.3 > > > > -- > Peter Xu -- Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
next prev parent reply other threads:[~2018-05-02 15:30 UTC|newest] Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top 2018-04-28 8:10 [PATCH] migration: fix saving normal page even if it's been compressed guangrong.xiao 2018-04-28 8:10 ` [Qemu-devel] " guangrong.xiao 2018-05-02 2:46 ` Peter Xu 2018-05-02 2:46 ` [Qemu-devel] " Peter Xu 2018-05-02 15:30 ` Dr. David Alan Gilbert [this message] 2018-05-02 15:30 ` Dr. David Alan Gilbert 2018-05-03 2:21 ` Peter Xu 2018-05-03 2:21 ` [Qemu-devel] " Peter Xu 2018-05-03 3:13 ` Xiao Guangrong 2018-05-03 3:13 ` [Qemu-devel] " Xiao Guangrong
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