Re: [Qemu-devel] [PATCH v2 3/5] migration: remove unnecessary variables len in QIOChannelRDMA

[858585 jemmy]

On Fri, Apr 27, 2018 at 12:40 AM, Dr. David Alan Gilbert
<address@hidden> wrote:
> * Lidong Chen (address@hidden) 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 <address@hidden>
>
> 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 <address@hidden>
>
>> ---
>>  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 / address@hidden / Manchester, UK