From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id C644B38D017 for ; Sat, 28 Feb 2026 18:09:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772302192; cv=none; b=mRWG9m0gd6/N7FVIzZfGKu59arrAdrHnBw4FjkNlQ3qC4kvupK9wYkGGPPmJydhhqTTDrQVtV1XyX2fiKQqioyjpbBKkdODsXhFPFiuA9nHnsXHSDauLzX5D3af4aVCO9HzUGQi3kaHLuVErOURlMrIsTQHQnUeRkIbV+viHYIg= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772302192; c=relaxed/simple; bh=lVV3ZKuMsSFYufrrr5+nZ/uyk0YeGGF9TdfcVXlFgQk=; h=From:To:Cc:Subject:Date:Message-ID:In-Reply-To:References: MIME-Version; b=DABAxqIa82J/3ghEvsvqg1JkiiN2fQbGzjK0/8gZSP7NYf72PNc1aErUBXfS8YaBKnpI8zC94HIsDimLp6oMiuYLF89JL2M6KU24zwQgyf7uBenA1GSzbbVMosreeemhqJ/RtlljX0UBgVCGa6UxvgFEBmwP6GfuYKGyOHUzV3Y= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=oePORSh1; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="oePORSh1" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 40962C19423; Sat, 28 Feb 2026 18:09:52 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1772302192; bh=lVV3ZKuMsSFYufrrr5+nZ/uyk0YeGGF9TdfcVXlFgQk=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=oePORSh1rgX+JXpgduACFoIrfgNiJzUhYLplemusGY/OhY0VDmZnmPwfD97itjh3X +zuzah03ZrvAU1X8JhLMNmpwymHThw64QjrI/nG10rgJRNaf6lwRV6kofhfWqahJWb y2GhhVpWC/Dkb8eG1AVoOTCKGhWRo79U7Yi7LuUEltKq8sV3y+QLljcRJR/Lq224jv YGflqs7R49Bu/bW6VMqU20NOCMRfyKzxRfyL6qmCVS21bVt5eDaa3DkK+2Y/voBK+1 gMwqYOsd4l8RKYS1sDy3IUCrxZIyfc4xDBtSS3gOR4yz+yGMleIeuGgOtaYOcNLTaV VWHEkzHSWJWdw== From: Sasha Levin To: patches@lists.linux.dev Cc: Chuck Lever , Sasha Levin Subject: [PATCH 6.6 195/283] svcrdma: Increase the per-transport rw_ctx count Date: Sat, 28 Feb 2026 13:05:37 -0500 Message-ID: <20260228180709.1583486-195-sashal@kernel.org> X-Mailer: git-send-email 2.51.0 In-Reply-To: <20260228180709.1583486-1-sashal@kernel.org> References: <20260228180709.1583486-1-sashal@kernel.org> Precedence: bulk X-Mailing-List: patches@lists.linux.dev List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit From: Chuck Lever [ Upstream commit 2da0f610e733606e06284ac3c1f188b9dec75d68 ] rdma_rw_mr_factor() returns the smallest number of MRs needed to move a particular number of pages. svcrdma currently asks for the number of MRs needed to move RPCSVC_MAXPAGES (a little over one megabyte), as that is the number of pages in the largest r/wsize the server supports. This call assumes that the client's NIC can bundle a full one megabyte payload in a single rdma_segment. In fact, most NICs cannot handle a full megabyte with a single rkey / rdma_segment. Clients will typically split even a single Read chunk into many segments. The server needs one MR to read each rdma_segment in a Read chunk, and thus each one needs an rw_ctx. svcrdma has been vastly underestimating the number of rw_ctxs needed to handle 64 RPC requests with large Read chunks using small rdma_segments. Unfortunately there doesn't seem to be a good way to estimate this number without knowing the client NIC's capabilities. Even then, the client RPC/RDMA implementation is still free to split a chunk into smaller segments (for example, it might be using physical registration, which needs an rdma_segment per page). The best we can do for now is choose a number that will guarantee forward progress in the worst case (one page per segment). At some later point, we could add some mechanisms to make this much less of a problem: - Add a core API to add more rw_ctxs to an already-established QP - svcrdma could treat rw_ctx exhaustion as a temporary error and try again - Limit the number of Reads in flight Signed-off-by: Chuck Lever Stable-dep-of: afcae7d7b8a2 ("RDMA/core: add rdma_rw_max_sge() helper for SQ sizing") Signed-off-by: Sasha Levin --- net/sunrpc/xprtrdma/svc_rdma_transport.c | 9 +++++++-- 1 file changed, 7 insertions(+), 2 deletions(-) diff --git a/net/sunrpc/xprtrdma/svc_rdma_transport.c b/net/sunrpc/xprtrdma/svc_rdma_transport.c index e26d1a7035e55..41db2b1ee0d13 100644 --- a/net/sunrpc/xprtrdma/svc_rdma_transport.c +++ b/net/sunrpc/xprtrdma/svc_rdma_transport.c @@ -415,8 +415,13 @@ static struct svc_xprt *svc_rdma_accept(struct svc_xprt *xprt) newxprt->sc_max_requests = rq_depth - 2; newxprt->sc_max_bc_requests = 2; } - ctxts = rdma_rw_mr_factor(dev, newxprt->sc_port_num, RPCSVC_MAXPAGES); - ctxts *= newxprt->sc_max_requests; + + /* Arbitrarily estimate the number of rw_ctxs needed for + * this transport. This is enough rw_ctxs to make forward + * progress even if the client is using one rkey per page + * in each Read chunk. + */ + ctxts = 3 * RPCSVC_MAXPAGES; newxprt->sc_sq_depth = rq_depth + ctxts; if (newxprt->sc_sq_depth > dev->attrs.max_qp_wr) newxprt->sc_sq_depth = dev->attrs.max_qp_wr; -- 2.51.0