> On 29 May 2018, at 18:40, Jason Gunthorpe <jgg@xxxxxxxx> wrote: > > On Tue, May 29, 2018 at 06:16:14PM +0200, Håkon Bugge wrote: >> >>> On 29 May 2018, at 17:49, Jason Gunthorpe <jgg@xxxxxxxx> wrote: >>> >>> On Tue, May 29, 2018 at 09:38:08AM +0200, Hans Westgaard Ry wrote: >>>> The agent TID is a 64 bit value split in two dwords. The least >>>> significant dword is the TID running counter. The most significant >>>> dword is the agent number. In the CX-3 shared port model, the mlx4 >>>> driver uses the most significant byte of the agent number to store the >>>> slave number, making agent numbers greater and equal to 2^24 (3 bytes) >>>> unusable. >>> >>> There is no reason for this to be an ida, just do something like >>> >>> mad_agent_priv->agent.hi_tid = atomic_inc_return(&ib_mad_client_id) & mad_agent_priv->ib_dev->tid_mask; >>> >>> And have the driver set tid_mask to 3 bytes of 0xFF >> >> The issue is that some of the mad agents are long-lived, so you will >> wrap and use the same TID twice. > > We already have that problem, and using ida is problematic because we > need to maximize the time between TID re-use, which ida isn't doing. Initially, I thought that too, but consulted the spec which states: C13-18.1.1: When initiating a new operation, MADHeader:TransactionID shall be set to such a value that within that MAD the combination of TID, SGID, and MgmtClass is different from that of any other currently executing operation. [] "currently executing operation" that is. But if timeouts etc. leads to MAD floating around in the fabric, its of course more robust to maximize the time between reuse. Then idr_alloc_cyclic() can be used. > Preventing re-use seems like a seperate issue from limiting the range > to be compatible with mlx4. Yes. But a v2 of Hans' patch using idr_alloc_cyclic() solves both issues. Thxs, Håkon > > Jason > -- > To unsubscribe from this list: send the line "unsubscribe linux-rdma" in > the body of a message to majordomo@xxxxxxxxxxxxxxx > More majordomo info at http://vger.kernel.org/majordomo-info.html -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
