On 01/13/2015 08:18 PM, Ben England wrote: > Rafi, > > it totally makes sense to me that you need to pre-allocate i/o buffers that will be used by RDMA, and you don't want to constantly change (i.e. allocate and deallocate) these buffers. Since a remote RDMA controller can be reading and writing to them, we have to be very careful about deallocating in particular. So an "arena" of pre-registered RDMA buffers makes perfect sense. > > Am I understanding you correctly that io-cache translator is soaking up all the RDMA-related buffers? Yes, If a page fault is generated for an inode, then in the call back of the request,we will take a ref on that iobref and will cache that iobufs in a rbtree. > How important is io-cache translator to Gluster performance at this point? Given that FUSE caching is now enabled, it seems to me that io-cache translator would accomplish very little. Should we have it disabled by default? I'm not sure about the performance enhancement given by io-cache > If so, would that solve your problem? Yes. Though, theoretically there is a chance for running out of default iobufs, but that is tolerable as long as some one is not holding the iobufs for indefinitely > > So how do read-ahead translator and write-behind translator interact with RDMA buffering? All of this translator will take buffer from the same pool, but they are not holding the buffer for so long. For reah-ahead, If the next request is not received or if it is not sequential read, read-ahead translator will drop the data. So always that buffers are available for rdma. Regards Rafi KC > > -ben > > ----- Original Message ----- >> From: "Mohammed Rafi K C" <rkavunga@xxxxxxxxxx> >> To: gluster-devel@xxxxxxxxxxx >> Sent: Tuesday, January 13, 2015 9:29:56 AM >> Subject: Suggestion needed to make use of iobuf_pool as rdma buffer. >> >> Hi All, >> >> When using RDMA protocol, we need to register the buffer which is going >> to send through rdma with rdma device. In fact, it is a costly >> operation, and a performance killer if it happened in I/O path. So our >> current plan is to register pre-allocated iobuf_arenas from iobuf_pool >> with rdma when rdma is getting initialized. The problem comes when all >> the iobufs are exhausted, then we need to dynamically allocate new >> arenas from libglusterfs module. Since it is created in libglusterfs, we >> can't make a call to rdma from libglusterfs. So we will force to >> register each of the iobufs from the newly created arenas with rdma in >> I/O path. If io-cache is turned on in client stack, then all the >> pre-registred arenas will use by io-cache as cache buffer. so we have to >> do the registration in rdma for each i/o call for every iobufs, >> eventually we cannot make use of pre registered arenas. >> >> To address the issue, we have two approaches in mind, >> >> 1) Register each dynamically created buffers in iobuf by bringing >> transport layer together with libglusterfs. >> >> 2) create a separate buffer for caching and offload the data from the >> read response to the cache buffer in background. >> >> If we could make use of preregister memory for every rdma call, then we >> will have approximately 20% increment for write and 25% of increment for >> read. >> >> Please give your thoughts to address the issue. >> >> Thanks & Regards >> Rafi KC >> _______________________________________________ >> Gluster-devel mailing list >> Gluster-devel@xxxxxxxxxxx >> http://www.gluster.org/mailman/listinfo/gluster-devel >> _______________________________________________ Gluster-devel mailing list Gluster-devel@xxxxxxxxxxx http://www.gluster.org/mailman/listinfo/gluster-devel
