From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 5E8C925785C; Thu, 25 Jun 2026 17:46:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782409609; cv=none; b=sWH3Y6qobqoxNJm5C2ruxM+05WVynhDVWh1JPJsR+ZKmDrddBrVahgmqgQ9G8DDEMuvnmtXqyCTC8nzVvFXgW+2Ty0EjQEZpL2eQnFYDXRtRZtjyFjepW1UyF1SsOLn9KQyFjOR2kGh7uZWBgn27NAX+PfTSDKPtdO1s9I4PSjQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1782409609; c=relaxed/simple; bh=O3P0LjkdvO3lnZ9rvJp9sA4O3eCjIHpgJD8XIHauBZo=; h=Date:From:To:cc:Subject:In-Reply-To:Message-ID:References: MIME-Version:Content-Type; b=Kxm0A/7DgTzhp6evh9g37w1jraInotbAvmj0wDZp6b+0o+s5WtcbR8EYnhBhRQDnEAuPyp5bBsA346+AFYp5PY+ogdgEApb50264/QRtqmFtzhwy7YQdJ9yxImKYHjx0lGzb6o/UgxcBfA/HDmsNv2dmvtoovE4TkXj4VVivNFI= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=RSxNHB+I; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="RSxNHB+I" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 66E491F000E9; Thu, 25 Jun 2026 17:46:46 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1782409607; bh=w23cGRwX5IS5ZlV/pHDg+qB9kyiLmObqHEcTd7CFGvE=; h=Date:From:To:cc:Subject:In-Reply-To:References; b=RSxNHB+I/jJ6qw68tDzeZ0HpNAd3bQ2HvGV3wH3O/18mgX+h/UtaOFhRITFT2osRC bKNk25wjyIN9oA8t2OKZNunclmHovblhWWyNGeQ5r2bS1kaQ6A5b+FJDVYvH2nw1B8 WyLqeK5FbAakQaS9Btzgy5N63fGNOfKQyqeqLF7fWHY67Vo2UNgkHsWVHymAXwqqFB TZZLUv+0sNz7RsuhoIwBBK3CNQIjyAd96R+8uC/EFUBZxCnAipbXNhXPH2vp3pMfpH O4348o0IDW9aPKaBpoRfWe/hFsspmm5o7wksXQ3kRB2Bm+JhJv3xJGxSP83mJTZ61I 3fB30qhuvsirw== Date: Thu, 25 Jun 2026 11:46:42 -0600 (MDT) From: Paul Walmsley To: Vivian Wang cc: Drew Fustini , Paul Walmsley , Palmer Dabbelt , Alexandre Ghiti , Yixun Lan , linux-riscv@lists.infradead.org, linux-kernel@vger.kernel.org, spacemit@lists.linux.dev, Lufei Zheng , Han Gao Subject: Re: [PATCH] riscv: Raise default NR_CPUS for 64BIT to 256 In-Reply-To: <20260625-riscv-more-nr-cpus-v1-1-5da8c72b9269@iscas.ac.cn> Message-ID: <825bb878-b5d8-7bdd-c5fe-744fc7f8e05c@kernel.org> References: <20260625-riscv-more-nr-cpus-v1-1-5da8c72b9269@iscas.ac.cn> Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII On Thu, 25 Jun 2026, Vivian Wang wrote: > SpacemiT has already produced a 80-core RVA23 RISC-V server [1], and > going further back, the dual-socket SG2042-based Sophgo Pisces has 128 > cores (although that had some issues achieving mainline support). > Therefore, an NR_CPUS of 64 is not enough. > > Raise default NR_CPUS to 256 for 64BIT (when !RISCV_SBI_V01, since very > old firmware can't support more than 64 cores). The number was picked as > a power of two that is at least double the known max. I believe this > should be the right balance between not wasting too much memory and not > having to touch this too often. > > Ubuntu has already been shipping NR_CPUS=512 for riscv64. We have also > been testing NR_CPUS=256 internally at ISCAS and found negligible > performance impact and no ill effects. > > Reported-by: Lufei Zheng > Link: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=1140651 # [1] > Suggested-by: Han Gao > Signed-off-by: Vivian Wang Thanks, queued for v7.2-rc. - Paul