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dpif-netdev: Clarify PMD reloading scheme.

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It became more complicated, hence needs to be documented.

Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>
This commit is contained in:
Ilya Maximets 2019-07-10 14:50:52 +03:00 committed by Ian Stokes
parent 68a0625b78
commit ec61d4707b
1 changed files with 39 additions and 0 deletions
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39
lib/dpif-netdev.c
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@ -682,10 +682,49 @@ struct dp_netdev_pmd_thread {
struct seq *reload_seq;
uint64_t last_reload_seq;
/* These are atomic variables used as a synchronization and configuration
* points for thread reload/exit.
*
* 'reload' atomic is the main one and it's used as a memory
* synchronization point for all other knobs and data.
*
* For a thread that requests PMD reload:
*
* * All changes that should be visible to the PMD thread must be made
* before setting the 'reload'. These changes could use any memory
* ordering model including 'relaxed'.
* * Setting the 'reload' atomic should occur in the same thread where
* all other PMD configuration options updated.
* * Setting the 'reload' atomic should be done with 'release' memory
* ordering model or stricter. This will guarantee that all previous
* changes (including non-atomic and 'relaxed') will be visible to
* the PMD thread.
* * To check that reload is done, thread should poll the 'reload' atomic
* to become 'false'. Polling should be done with 'acquire' memory
* ordering model or stricter. This ensures that PMD thread completed
* the reload process.
*
* For the PMD thread:
*
* * PMD thread should read 'reload' atomic with 'acquire' memory
* ordering model or stricter. This will guarantee that all changes
* made before setting the 'reload' in the requesting thread will be
* visible to the PMD thread.
* * All other configuration data could be read with any memory
* ordering model (including non-atomic and 'relaxed') but *only after*
* reading the 'reload' atomic set to 'true'.
* * When the PMD reload done, PMD should (optionally) set all the below
* knobs except the 'reload' to their default ('false') values and
* (mandatory), as the last step, set the 'reload' to 'false' using
* 'release' memory ordering model or stricter. This will inform the
* requesting thread that PMD has completed a reload cycle.
*/
atomic_bool reload; /* Do we need to reload ports? */
atomic_bool wait_for_reload; /* Can we busy wait for the next reload? */
atomic_bool reload_tx_qid; /* Do we need to reload static_tx_qid? */
atomic_bool exit; /* For terminating the pmd thread. */
pthread_t thread;
unsigned core_id; /* CPU core id of this pmd thread. */
int numa_id; /* numa node id of this pmd thread. */