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 E4FA81F3B97 for ; Mon, 3 Mar 2025 20:39:03 +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=1741034344; cv=none; b=eWkY+XTcBjjIq1okNwaj6FTkC4PQ3gcDJ8qlDu2GxvORJW7YlC0w6VgdV8lGnQ1Jg+dyUGsO1wb9SM80BdhEGWe9i2d3ZBNVNBbxjl6kfZ7ZTYgS45LxmMWberWPnndLwIIf3NgIb9IeSY87r4AHPbDe5R5WGYcJK4QX5F0LI90= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1741034344; c=relaxed/simple; bh=FKAENEmdxRxO0niyYat4E6UU2NzH/B8FWEUJNxcOZXk=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=mHbyM4YiZV+rMmoATh3qccijO0FdkFd5qz/9xSdHYoF69/ABfQDrd3WoNHZjc7c2GKk8ntgFK/KCsxU62cxbphxcb0y+quSXEk946IkNhVZbtdQOIlduzOm/Cgb3M6zMH6qbmPqxbB+IsNtbiyRB40hUlUdKvYJd2aWaJIkJgK8= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=A5geYHre; 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="A5geYHre" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 83CE8C4CED6; Mon, 3 Mar 2025 20:39:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1741034343; bh=FKAENEmdxRxO0niyYat4E6UU2NzH/B8FWEUJNxcOZXk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=A5geYHremFVRHjmjiqtTuFyBmo5uHhb2y2SVrAcPjJfno6mPsvjtcHv+5gt94fK6o q0oTl18wifT2E+j8cQ9f3Dgrgi0OSrsH4cLzOSqRwfkKq0Vkc/xNuhDutCX8wimNlf MLD660xKZRX62DS0JohYmuVqR1XOfuPKc7N7Yi18BN+RpP9MYzThWhc5bpGgK3Jd05 iutjxVoZmZYh1qNVK5120feERnMi0bjLyAjUIvwKJPZSVChO82cdZqn8TexcdUeipI cqfonDSYID9sinn2uMIca3iR43c7ZVcvXfG175n5tgPX8AAlqQ2PywhIGv41mFU0cv +N5ICzmh52G+w== Date: Mon, 3 Mar 2025 21:38:57 +0100 From: Ingo Molnar To: Brian Gerst Cc: linux-kernel@vger.kernel.org, x86@kernel.org, "H . Peter Anvin" , Thomas Gleixner , Borislav Petkov , Ard Biesheuvel , Uros Bizjak , Linus Torvalds , Andy Lutomirski , Peter Zijlstra , Andrew Morton Subject: Re: [PATCH v3 00/11] Add a percpu subsection for cache hot data Message-ID: References: <20250303165246.2175811-1-brgerst@gmail.com> 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 Content-Disposition: inline In-Reply-To: <20250303165246.2175811-1-brgerst@gmail.com> * Brian Gerst wrote: > Add a new percpu subsection for data that is frequently accessed and > exclusive to each processor. This replaces the pcpu_hot struct on x86, > and is available to all architectures and the core kernel. > > ffffffff834f5000 D __per_cpu_hot_start > ffffffff834f5000 D hardirq_stack_ptr > ffffffff834f5008 D __ref_stack_chk_guard > ffffffff834f5008 D __stack_chk_guard > ffffffff834f5010 D const_cpu_current_top_of_stack > ffffffff834f5010 D cpu_current_top_of_stack > ffffffff834f5018 D const_current_task > ffffffff834f5018 D current_task > ffffffff834f5020 D __x86_call_depth > ffffffff834f5028 D this_cpu_off > ffffffff834f5030 D __preempt_count > ffffffff834f5034 D cpu_number > ffffffff834f5038 D __softirq_pending > ffffffff834f503a D hardirq_stack_inuse > ffffffff834f503b D __per_cpu_hot_pad > ffffffff834f5040 D __per_cpu_hot_end > > This applies to the tip/x86/asm branch. > > Changes in v3: > - Fix typo of CACHE_HOT_DATA() > - Move hardirq_stack_inuse to irq_64.c > - Add __per_cpu_hot_pad to show the end of the actual data > > Brian Gerst (11): > percpu: Introduce percpu hot section > x86/percpu: Move pcpu_hot to percpu hot section > x86/preempt: Move preempt count to percpu hot section > x86/smp: Move cpu number to percpu hot section > x86/retbleed: Move call depth to percpu hot section > x86/softirq: Move softirq_pending to percpu hot section > x86/irq: Move irq stacks to percpu hot section > x86/percpu: Move top_of_stack to percpu hot section > x86/percpu: Move current_task to percpu hot section > x86/stackprotector: Move __stack_chk_guard to percpu hot section > x86/smp: Move this_cpu_off to percpu hot section > 31 files changed, 146 insertions(+), 111 deletions(-) Yeah, so the result is that on x86-64 allmodconfig we now get: ld: percpu cache hot section too large See the relevant .tmp_vmlinux1.map below. Which is due to: CONFIG_X86_INTERNODE_CACHE_SHIFT=12 Increasing 'cache alignment' to 4096 bytes: PERCPU_SECTION(INTERNODE_CACHE_BYTES) ... because of the vSMP muck: config X86_INTERNODE_CACHE_SHIFT int default "12" if X86_VSMP default X86_L1_CACHE_SHIFT The workaround would be to use L1_CACHE_BYTES in, but I really dislike what vSMP is doing here. Anyway, I applied the short-term fix to patch 02/11, but I'm not sure it's the right fix. Thanks, Ingo =====================> 0xffffffff8664f000 . = ALIGN (0x1000) 0xffffffff8664f000 __per_cpu_hot_start = . *(SORT_BY_ALIGNMENT(.data..percpu..hot.*)) .data..percpu..hot..hardirq_stack_ptr 0xffffffff8664f000 0x8 vmlinux.o 0xffffffff8664f000 hardirq_stack_ptr .data..percpu..hot..__stack_chk_guard 0xffffffff8664f008 0x8 vmlinux.o 0xffffffff8664f008 __stack_chk_guard .data..percpu..hot..cpu_current_top_of_stack 0xffffffff8664f010 0x8 vmlinux.o 0xffffffff8664f010 cpu_current_top_of_stack .data..percpu..hot..current_task 0xffffffff8664f018 0x8 vmlinux.o 0xffffffff8664f018 current_task .data..percpu..hot..__x86_call_depth 0xffffffff8664f020 0x8 vmlinux.o 0xffffffff8664f020 __x86_call_depth .data..percpu..hot..this_cpu_off 0xffffffff8664f028 0x8 vmlinux.o 0xffffffff8664f028 this_cpu_off .data..percpu..hot..__preempt_count 0xffffffff8664f030 0x4 vmlinux.o 0xffffffff8664f030 __preempt_count .data..percpu..hot..cpu_number 0xffffffff8664f034 0x4 vmlinux.o 0xffffffff8664f034 cpu_number .data..percpu..hot..__softirq_pending 0xffffffff8664f038 0x2 vmlinux.o 0xffffffff8664f038 __softirq_pending .data..percpu..hot..hardirq_stack_inuse 0xffffffff8664f03a 0x1 vmlinux.o 0xffffffff8664f03a hardirq_stack_inuse 0xffffffff8664f03b __per_cpu_hot_pad = . 0xffffffff86650000 . = ALIGN (0x1000) *fill* 0xffffffff8664f03b 0xfc5 0xffffffff86650000 __per_cpu_hot_end = . *(.data..percpu..read_mostly) .data..percpu..read_mostly 0xffffffff86650000 0xa30 vmlinux.o =================> arch/x86/kernel/vmlinux.lds.S | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S index 9ac6b42701fa..31f9102b107f 100644 --- a/arch/x86/kernel/vmlinux.lds.S +++ b/arch/x86/kernel/vmlinux.lds.S @@ -330,7 +330,7 @@ SECTIONS EXIT_DATA } - PERCPU_SECTION(INTERNODE_CACHE_BYTES) + PERCPU_SECTION(L1_CACHE_BYTES) ASSERT(__per_cpu_hot_end - __per_cpu_hot_start <= 64, "percpu cache hot section too large") RUNTIME_CONST_VARIABLES