Re: [PATCH v6 01/13] multifd: Document the locking of MultiFD{Send/Recv}Params

[Dr. David Alan Gilbert]

* Juan Quintela (quintela@redhat.com) wrote:
> Reorder the structures so we can know if the fields are:
> - Read only
> - Their own locking (i.e. sems)
> - Protected by 'mutex'
> - Only for the multifd channel
> 
> Signed-off-by: Juan Quintela <quintela@redhat.com>
> ---
>  migration/multifd.h | 86 +++++++++++++++++++++++++++------------------
>  1 file changed, 51 insertions(+), 35 deletions(-)
> 
> diff --git a/migration/multifd.h b/migration/multifd.h
> index 7d0effcb03..f1f88c6737 100644
> --- a/migration/multifd.h
> +++ b/migration/multifd.h
> @@ -65,7 +65,9 @@ typedef struct {
>  } MultiFDPages_t;
>  
>  typedef struct {
> -    /* this fields are not changed once the thread is created */
> +    /* Fiields are only written at creating/deletion time */
> +    /* No lock required for them, they are read only */
> +
>      /* channel number */
>      uint8_t id;
>      /* channel thread name */
> @@ -74,37 +76,45 @@ typedef struct {
>      QemuThread thread;
>      /* communication channel */
>      QIOChannel *c;
> -    /* sem where to wait for more work */
> -    QemuSemaphore sem;
> -    /* this mutex protects the following parameters */
> -    QemuMutex mutex;
> -    /* is this channel thread running */
> -    bool running;
> -    /* should this thread finish */
> -    bool quit;
>      /* is the yank function registered */
>      bool registered_yank;
> +    /* packet allocated len */
> +    uint32_t packet_len;
> +
> +    /* sem where to wait for more work */
> +    QemuSemaphore sem;
> +    /* syncs main thread and channels */
> +    QemuSemaphore sem_sync;
> +
> +    /* this mutex protects the following parameters */
> +    QemuMutex mutex;
> +    /* is this channel thread running */
> +    bool running;
> +    /* should this thread finish */
> +    bool quit;
> +    /* multifd flags for each packet */
> +    uint32_t flags;
> +    /* global number of generated multifd packets */
> +    uint64_t packet_num;

Is there a way to explain why packet_num, being global, is inside
SendParams?  I understand why num_packets is - because
that's per channel; so why is a global isnide the params
(and having two things with almost the same name is very confusing!)

Dave

>      /* thread has work to do */
>      int pending_job;
> -    /* array of pages to sent */
> +    /* array of pages to sent.
> +     * The owner of 'pages' depends of 'pending_job' value:
> +     * pending_job == 0 -> migration_thread can use it.
> +     * pending_job != 0 -> multifd_channel can use it.
> +     */
>      MultiFDPages_t *pages;
> -    /* packet allocated len */
> -    uint32_t packet_len;
> +
> +    /* thread local variables. No locking required */
> +
>      /* pointer to the packet */
>      MultiFDPacket_t *packet;
> -    /* multifd flags for each packet */
> -    uint32_t flags;
>      /* size of the next packet that contains pages */
>      uint32_t next_packet_size;
> -    /* global number of generated multifd packets */
> -    uint64_t packet_num;
> -    /* thread local variables */
>      /* packets sent through this channel */
>      uint64_t num_packets;
>      /* non zero pages sent through this channel */
>      uint64_t total_normal_pages;
> -    /* syncs main thread and channels */
> -    QemuSemaphore sem_sync;
>      /* buffers to send */
>      struct iovec *iov;
>      /* number of iovs used */
> @@ -118,7 +128,9 @@ typedef struct {
>  }  MultiFDSendParams;
>  
>  typedef struct {
> -    /* this fields are not changed once the thread is created */
> +    /* Fiields are only written at creating/deletion time */
> +    /* No lock required for them, they are read only */
> +
>      /* channel number */
>      uint8_t id;
>      /* channel thread name */
> @@ -127,31 +139,35 @@ typedef struct {
>      QemuThread thread;
>      /* communication channel */
>      QIOChannel *c;
> +    /* packet allocated len */
> +    uint32_t packet_len;
> +
> +    /* syncs main thread and channels */
> +    QemuSemaphore sem_sync;
> +
>      /* this mutex protects the following parameters */
>      QemuMutex mutex;
>      /* is this channel thread running */
>      bool running;
>      /* should this thread finish */
>      bool quit;
> +    /* multifd flags for each packet */
> +    uint32_t flags;
> +    /* global number of generated multifd packets */
> +    uint64_t packet_num;
> +
> +    /* thread local variables. No locking required */
> +
> +    /* pointer to the packet */
> +    MultiFDPacket_t *packet;
> +    /* size of the next packet that contains pages */
> +    uint32_t next_packet_size;
> +    /* packets sent through this channel */
> +    uint64_t num_packets;
>      /* ramblock host address */
>      uint8_t *host;
> -    /* packet allocated len */
> -    uint32_t packet_len;
> -    /* pointer to the packet */
> -    MultiFDPacket_t *packet;
> -    /* multifd flags for each packet */
> -    uint32_t flags;
> -    /* global number of generated multifd packets */
> -    uint64_t packet_num;
> -    /* thread local variables */
> -    /* size of the next packet that contains pages */
> -    uint32_t next_packet_size;
> -    /* packets sent through this channel */
> -    uint64_t num_packets;
>      /* non zero pages recv through this channel */
>      uint64_t total_normal_pages;
> -    /* syncs main thread and channels */
> -    QemuSemaphore sem_sync;
>      /* buffers to recv */
>      struct iovec *iov;
>      /* Pages that are not zero */
> -- 
> 2.35.1
> 
-- 
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK