From: Ned Bass <bass6@xxxxxxxx> As this lock can be a bottleneck, clarifying why it is needed may be helpful to those working on client performance. Signed-off-by: Ned Bass <bass6@xxxxxxxx> Intel-bug-id: https://jira.hpdd.intel.com/browse/LU-3443 Reviewed-on: http://review.whamcloud.com/6593 Reviewed-by: Andreas Dilger <andreas.dilger@xxxxxxxxx> Reviewed-by: Keith Mannthey <keith.mannthey@xxxxxxxxx> Signed-off-by: James Simmons <jsimmons@xxxxxxxxxxxxx> --- drivers/staging/lustre/lustre/include/lustre_mdc.h | 18 ++++++++++++++++++ 1 files changed, 18 insertions(+), 0 deletions(-) diff --git a/drivers/staging/lustre/lustre/include/lustre_mdc.h b/drivers/staging/lustre/lustre/include/lustre_mdc.h index df94f9f..9e54790 100644 --- a/drivers/staging/lustre/lustre/include/lustre_mdc.h +++ b/drivers/staging/lustre/lustre/include/lustre_mdc.h @@ -64,9 +64,27 @@ struct obd_export; struct ptlrpc_request; struct obd_device; +/** + * Serializes in-flight MDT-modifying RPC requests to preserve idempotency. + * + * This mutex is used to implement execute-once semantics on the MDT. + * The MDT stores the last transaction ID and result for every client in + * its last_rcvd file. If the client doesn't get a reply, it can safely + * resend the request and the MDT will reconstruct the reply being aware + * that the request has already been executed. Without this lock, + * execution status of concurrent in-flight requests would be + * overwritten. + * + * This design limits the extent to which we can keep a full pipeline of + * in-flight requests from a single client. This limitation could be + * overcome by allowing multiple slots per client in the last_rcvd file. + */ struct mdc_rpc_lock { + /** Lock protecting in-flight RPC concurrency. */ struct mutex rpcl_mutex; + /** Intent associated with currently executing request. */ struct lookup_intent *rpcl_it; + /** Used for MDS/RPC load testing purposes. */ int rpcl_fakes; }; -- 1.7.1 _______________________________________________ devel mailing list devel@xxxxxxxxxxxxxxxxxxxxxx http://driverdev.linuxdriverproject.org/mailman/listinfo/driverdev-devel
