diff mbox series

[v2,3/5] migration: remove unnecessary variables len in QIOChannelRDMA

Message ID 1524666934-8064-4-git-send-email-lidongchen@tencent.com
State New
Headers show
Series Enable postcopy RDMA live migration | expand

Commit Message

858585 jemmy April 25, 2018, 2:35 p.m. UTC 
Because qio_channel_rdma_writev and qio_channel_rdma_readv maybe invoked
by different threads concurrently, this patch removes unnecessary variables
len in QIOChannelRDMA and use local variable instead.

Signed-off-by: Lidong Chen <lidongchen@tencent.com>
---
 migration/rdma.c | 15 +++++++--------
 1 file changed, 7 insertions(+), 8 deletions(-)

Comments

Dr. David Alan Gilbert April 26, 2018, 4:40 p.m. UTC | #1 
* Lidong Chen (jemmy858585@gmail.com) wrote:
> Because qio_channel_rdma_writev and qio_channel_rdma_readv maybe invoked
> by different threads concurrently, this patch removes unnecessary variables
> len in QIOChannelRDMA and use local variable instead.
> 
> Signed-off-by: Lidong Chen <lidongchen@tencent.com>

I'm OK with this patch as is; but now you're making me worried that I
don't quite understand what thrads are accessing it at the same time; we
need to document/comment what's accessed concurrently.

Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>

> ---
>  migration/rdma.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)
> 
> diff --git a/migration/rdma.c b/migration/rdma.c
> index c745427..f5c1d02 100644
> --- a/migration/rdma.c
> +++ b/migration/rdma.c
> @@ -404,7 +404,6 @@ struct QIOChannelRDMA {
>      QIOChannel parent;
>      RDMAContext *rdma;
>      QEMUFile *file;
> -    size_t len;
>      bool blocking; /* XXX we don't actually honour this yet */
>  };
>  
> @@ -2640,6 +2639,7 @@ static ssize_t qio_channel_rdma_writev(QIOChannel *ioc,
>      int ret;
>      ssize_t done = 0;
>      size_t i;
> +    size_t len = 0;
>  
>      CHECK_ERROR_STATE();
>  
> @@ -2659,10 +2659,10 @@ static ssize_t qio_channel_rdma_writev(QIOChannel *ioc,
>          while (remaining) {
>              RDMAControlHeader head;
>  
> -            rioc->len = MIN(remaining, RDMA_SEND_INCREMENT);
> -            remaining -= rioc->len;
> +            len = MIN(remaining, RDMA_SEND_INCREMENT);
> +            remaining -= len;
>  
> -            head.len = rioc->len;
> +            head.len = len;
>              head.type = RDMA_CONTROL_QEMU_FILE;
>  
>              ret = qemu_rdma_exchange_send(rdma, &head, data, NULL, NULL, NULL);
> @@ -2672,8 +2672,8 @@ static ssize_t qio_channel_rdma_writev(QIOChannel *ioc,
>                  return ret;
>              }
>  
> -            data += rioc->len;
> -            done += rioc->len;
> +            data += len;
> +            done += len;
>          }
>      }
>  
> @@ -2768,8 +2768,7 @@ static ssize_t qio_channel_rdma_readv(QIOChannel *ioc,
>              }
>          }
>      }
> -    rioc->len = done;
> -    return rioc->len;
> +    return done;
>  }
>  
>  /*
> -- 
> 1.8.3.1
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
858585 jemmy April 27, 2018, 3:51 a.m. UTC | #2 
On Fri, Apr 27, 2018 at 12:40 AM, Dr. David Alan Gilbert
<dgilbert@redhat.com> wrote:
> * Lidong Chen (jemmy858585@gmail.com) wrote:
>> Because qio_channel_rdma_writev and qio_channel_rdma_readv maybe invoked
>> by different threads concurrently, this patch removes unnecessary variables
>> len in QIOChannelRDMA and use local variable instead.
>>
>> Signed-off-by: Lidong Chen <lidongchen@tencent.com>
>
> I'm OK with this patch as is; but now you're making me worried that I
> don't quite understand what thrads are accessing it at the same time; we
> need to document/comment what's accessed concurrently..

for the source qemu, migration thread invokes qio_channel_rdma_writev,
and the return
path thread invokes qio_channel_rdma_readv.

for the destination qemu, before postcopy, the main thread invokes
qio_channel_rdma_readv
and qio_channel_rdma_writev.
after postcopy, the listen_thread invokes qio_channel_rdma_readv, and
the ram_fault_thread
invokes qio_channel_rdma_writev.

>
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
>
>> ---
>>  migration/rdma.c | 15 +++++++--------
>>  1 file changed, 7 insertions(+), 8 deletions(-)
>>
>> diff --git a/migration/rdma.c b/migration/rdma.c
>> index c745427..f5c1d02 100644
>> --- a/migration/rdma.c
>> +++ b/migration/rdma.c
>> @@ -404,7 +404,6 @@ struct QIOChannelRDMA {
>>      QIOChannel parent;
>>      RDMAContext *rdma;
>>      QEMUFile *file;
>> -    size_t len;
>>      bool blocking; /* XXX we don't actually honour this yet */
>>  };
>>
>> @@ -2640,6 +2639,7 @@ static ssize_t qio_channel_rdma_writev(QIOChannel *ioc,
>>      int ret;
>>      ssize_t done = 0;
>>      size_t i;
>> +    size_t len = 0;
>>
>>      CHECK_ERROR_STATE();
>>
>> @@ -2659,10 +2659,10 @@ static ssize_t qio_channel_rdma_writev(QIOChannel *ioc,
>>          while (remaining) {
>>              RDMAControlHeader head;
>>
>> -            rioc->len = MIN(remaining, RDMA_SEND_INCREMENT);
>> -            remaining -= rioc->len;
>> +            len = MIN(remaining, RDMA_SEND_INCREMENT);
>> +            remaining -= len;
>>
>> -            head.len = rioc->len;
>> +            head.len = len;
>>              head.type = RDMA_CONTROL_QEMU_FILE;
>>
>>              ret = qemu_rdma_exchange_send(rdma, &head, data, NULL, NULL, NULL);
>> @@ -2672,8 +2672,8 @@ static ssize_t qio_channel_rdma_writev(QIOChannel *ioc,
>>                  return ret;
>>              }
>>
>> -            data += rioc->len;
>> -            done += rioc->len;
>> +            data += len;
>> +            done += len;
>>          }
>>      }
>>
>> @@ -2768,8 +2768,7 @@ static ssize_t qio_channel_rdma_readv(QIOChannel *ioc,
>>              }
>>          }
>>      }
>> -    rioc->len = done;
>> -    return rioc->len;
>> +    return done;
>>  }
>>
>>  /*
>> --
>> 1.8.3.1
>>
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK
Daniel P. Berrangé April 27, 2018, 9:01 a.m. UTC | #3 
On Thu, Apr 26, 2018 at 05:40:11PM +0100, Dr. David Alan Gilbert wrote:
> * Lidong Chen (jemmy858585@gmail.com) wrote:
> > Because qio_channel_rdma_writev and qio_channel_rdma_readv maybe invoked
> > by different threads concurrently, this patch removes unnecessary variables
> > len in QIOChannelRDMA and use local variable instead.
> > 
> > Signed-off-by: Lidong Chen <lidongchen@tencent.com>
> 
> I'm OK with this patch as is; but now you're making me worried that I
> don't quite understand what thrads are accessing it at the same time; we
> need to document/comment what's accessed concurrently.

FWIW, I have always intended that QIOChannel impls be able to support
bidirectional I/O from multiple threads, provided they each are using
it in a different direction. So this is a mistake in my original RDMA
impl.

> 
> Reviewed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
> 
> > ---
> >  migration/rdma.c | 15 +++++++--------
> >  1 file changed, 7 insertions(+), 8 deletions(-)
> > 
> > diff --git a/migration/rdma.c b/migration/rdma.c
> > index c745427..f5c1d02 100644
> > --- a/migration/rdma.c
> > +++ b/migration/rdma.c
> > @@ -404,7 +404,6 @@ struct QIOChannelRDMA {
> >      QIOChannel parent;
> >      RDMAContext *rdma;
> >      QEMUFile *file;
> > -    size_t len;
> >      bool blocking; /* XXX we don't actually honour this yet */
> >  };
> >  
> > @@ -2640,6 +2639,7 @@ static ssize_t qio_channel_rdma_writev(QIOChannel *ioc,
> >      int ret;
> >      ssize_t done = 0;
> >      size_t i;
> > +    size_t len = 0;
> >  
> >      CHECK_ERROR_STATE();
> >  
> > @@ -2659,10 +2659,10 @@ static ssize_t qio_channel_rdma_writev(QIOChannel *ioc,
> >          while (remaining) {
> >              RDMAControlHeader head;
> >  
> > -            rioc->len = MIN(remaining, RDMA_SEND_INCREMENT);
> > -            remaining -= rioc->len;
> > +            len = MIN(remaining, RDMA_SEND_INCREMENT);
> > +            remaining -= len;
> >  
> > -            head.len = rioc->len;
> > +            head.len = len;
> >              head.type = RDMA_CONTROL_QEMU_FILE;
> >  
> >              ret = qemu_rdma_exchange_send(rdma, &head, data, NULL, NULL, NULL);
> > @@ -2672,8 +2672,8 @@ static ssize_t qio_channel_rdma_writev(QIOChannel *ioc,
> >                  return ret;
> >              }
> >  
> > -            data += rioc->len;
> > -            done += rioc->len;
> > +            data += len;
> > +            done += len;
> >          }
> >      }
> >  
> > @@ -2768,8 +2768,7 @@ static ssize_t qio_channel_rdma_readv(QIOChannel *ioc,
> >              }
> >          }
> >      }
> > -    rioc->len = done;
> > -    return rioc->len;
> > +    return done;
> >  }
> >  
> >  /*
> > -- 
> > 1.8.3.1
> > 
> --
> Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK

Regards,
Daniel
Daniel P. Berrangé April 27, 2018, 9:04 a.m. UTC | #4 
On Wed, Apr 25, 2018 at 10:35:32PM +0800, Lidong Chen wrote:
> Because qio_channel_rdma_writev and qio_channel_rdma_readv maybe invoked
> by different threads concurrently, this patch removes unnecessary variables
> len in QIOChannelRDMA and use local variable instead.
> 
> Signed-off-by: Lidong Chen <lidongchen@tencent.com>
> ---
>  migration/rdma.c | 15 +++++++--------
>  1 file changed, 7 insertions(+), 8 deletions(-)

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>


Regards,
Daniel
diff mbox series

Patch

diff --git a/migration/rdma.c b/migration/rdma.c
index c745427..f5c1d02 100644
--- a/migration/rdma.c
+++ b/migration/rdma.c
@@ -404,7 +404,6 @@  struct QIOChannelRDMA {
     QIOChannel parent;
     RDMAContext *rdma;
     QEMUFile *file;
-    size_t len;
     bool blocking; /* XXX we don't actually honour this yet */
 };
 
@@ -2640,6 +2639,7 @@  static ssize_t qio_channel_rdma_writev(QIOChannel *ioc,
     int ret;
     ssize_t done = 0;
     size_t i;
+    size_t len = 0;
 
     CHECK_ERROR_STATE();
 
@@ -2659,10 +2659,10 @@  static ssize_t qio_channel_rdma_writev(QIOChannel *ioc,
         while (remaining) {
             RDMAControlHeader head;
 
-            rioc->len = MIN(remaining, RDMA_SEND_INCREMENT);
-            remaining -= rioc->len;
+            len = MIN(remaining, RDMA_SEND_INCREMENT);
+            remaining -= len;
 
-            head.len = rioc->len;
+            head.len = len;
             head.type = RDMA_CONTROL_QEMU_FILE;
 
             ret = qemu_rdma_exchange_send(rdma, &head, data, NULL, NULL, NULL);
@@ -2672,8 +2672,8 @@  static ssize_t qio_channel_rdma_writev(QIOChannel *ioc,
                 return ret;
             }
 
-            data += rioc->len;
-            done += rioc->len;
+            data += len;
+            done += len;
         }
     }
 
@@ -2768,8 +2768,7 @@  static ssize_t qio_channel_rdma_readv(QIOChannel *ioc,
             }
         }
     }
-    rioc->len = done;
-    return rioc->len;
+    return done;
 }
 
 /*