From: Uros Bizjak <ubizjak@gmail.com>
To: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Nadav Amit <namit@vmware.com>,
"the arch/x86 maintainers" <x86@kernel.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andy Lutomirski <luto@kernel.org>,
Brian Gerst <brgerst@gmail.com>,
Denys Vlasenko <dvlasenk@redhat.com>,
"H . Peter Anvin" <hpa@zytor.com>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Josh Poimboeuf <jpoimboe@redhat.com>,
Nick Desaulniers <ndesaulniers@google.com>
Subject: Re: [PATCH v2 -tip] x86/percpu: Use C for arch_raw_cpu_ptr()
Date: Wed, 18 Oct 2023 19:07:45 +0200 [thread overview]
Message-ID: <CAFULd4YHq7tKQBNk9bNYZkBo9C5XM+6=O7QZG3E-qKBVjSHb6g@mail.gmail.com> (raw)
In-Reply-To: <CAHk-=wiB6LHPmnG7=RWNuQYY9=jCY0EmaJ7thRBEFOfDO09dfw@mail.gmail.com>
[-- Attachment #1: Type: text/plain, Size: 1334 bytes --]
On Wed, Oct 18, 2023 at 6:13 PM Linus Torvalds
<torvalds@linux-foundation.org> wrote:
>
> On Wed, 18 Oct 2023 at 06:15, Uros Bizjak <ubizjak@gmail.com> wrote:
> >
> > Attached is the prototype patch that works for me (together with
> > Linus' FPU switching patch).
>
> That looks reasonable, but I think the separate compilation unit is
> unnecessary, and I still absolutely hate how that const_pcpu_hot thing
> is declared twice (your patch does it in both current.h and in
> percpu-hot.c).
>
> How about we just do the whole alias as a linker thing instead? So the
> same way that we just do
>
> jiffies = jiffies_64;
>
> in our arch/x86/kernel/vmlinux.lds.S file, we could just do
>
> const_pcpu_hot = pcpu_hot;
>
> in there.
>
> Then, as far as the compiler is concerned, we just have
>
> DECLARE_PER_CPU_ALIGNED(
> const struct pcpu_hot __percpu_seg_override,
> const_pcpu_hot)
>
> and the compiler doesn't know that it's aliased to anything else.
Oh...
... this works, too! Please see the attached patch.
(Note to self: Leave linking stuff to linker) ;)
> And please do that declaration in just *one* place.
Sure. Now the patch looks quite slim, but works as expected, reducing
the number of current_task accesses from 3841 to 3220.
Thanks,
Uros.
[-- Attachment #2: current-2.diff.txt --]
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diff --git a/arch/x86/include/asm/current.h b/arch/x86/include/asm/current.h
index a1168e7b69e5..36902d61fd55 100644
--- a/arch/x86/include/asm/current.h
+++ b/arch/x86/include/asm/current.h
@@ -36,8 +36,17 @@ static_assert(sizeof(struct pcpu_hot) == 64);
DECLARE_PER_CPU_ALIGNED(struct pcpu_hot, pcpu_hot);
+/*
+ *
+ */
+DECLARE_PER_CPU_ALIGNED(const struct pcpu_hot __percpu_seg_override,
+ const_pcpu_hot);
+
static __always_inline struct task_struct *get_current(void)
{
+ if (IS_ENABLED(CONFIG_USE_X86_SEG_SUPPORT))
+ return const_pcpu_hot.current_task;
+
return this_cpu_read_stable(pcpu_hot.current_task);
}
diff --git a/arch/x86/kernel/vmlinux.lds.S b/arch/x86/kernel/vmlinux.lds.S
index 9cdb1a7332c4..7cbc42619e16 100644
--- a/arch/x86/kernel/vmlinux.lds.S
+++ b/arch/x86/kernel/vmlinux.lds.S
@@ -46,6 +46,7 @@ ENTRY(phys_startup_64)
#endif
jiffies = jiffies_64;
+const_pcpu_hot = pcpu_hot;
#if defined(CONFIG_X86_64)
/*
diff --git a/include/linux/compiler.h b/include/linux/compiler.h
index d7779a18b24f..bf9815eaf4aa 100644
--- a/include/linux/compiler.h
+++ b/include/linux/compiler.h
@@ -212,7 +212,7 @@ void ftrace_likely_update(struct ftrace_likely_data *f, int val,
*/
#define ___ADDRESSABLE(sym, __attrs) \
static void * __used __attrs \
- __UNIQUE_ID(__PASTE(__addressable_,sym)) = (void *)&sym;
+ __UNIQUE_ID(__PASTE(__addressable_,sym)) = (void *)(uintptr_t)&sym;
#define __ADDRESSABLE(sym) \
___ADDRESSABLE(sym, __section(".discard.addressable"))
next prev parent reply other threads:[~2023-10-18 17:24 UTC|newest]
Thread overview: 106+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-10-10 16:42 [PATCH v2 -tip] x86/percpu: Use C for arch_raw_cpu_ptr() Uros Bizjak
2023-10-10 17:32 ` Linus Torvalds
2023-10-10 18:22 ` Uros Bizjak
2023-10-10 18:25 ` Nadav Amit
2023-10-10 18:42 ` Linus Torvalds
2023-10-10 18:37 ` Linus Torvalds
2023-10-10 18:41 ` Uros Bizjak
2023-10-10 18:52 ` Linus Torvalds
2023-10-11 7:27 ` Uros Bizjak
2023-10-11 7:45 ` Uros Bizjak
2023-10-11 19:40 ` Linus Torvalds
2023-10-11 18:42 ` Uros Bizjak
2023-10-11 19:51 ` Linus Torvalds
2023-10-11 19:52 ` Linus Torvalds
2023-10-11 20:00 ` Uros Bizjak
2023-10-11 22:37 ` Ingo Molnar
2023-10-11 23:15 ` H. Peter Anvin
2023-10-12 1:35 ` Josh Poimboeuf
2023-10-12 6:19 ` Ingo Molnar
2023-10-12 16:08 ` Josh Poimboeuf
2023-10-12 17:59 ` Ingo Molnar
2023-10-12 21:30 ` Josh Poimboeuf
2023-10-13 10:52 ` Ingo Molnar
2023-10-11 7:41 ` Nadav Amit
2023-10-11 19:37 ` Linus Torvalds
2023-10-11 21:32 ` Uros Bizjak
2023-10-11 21:54 ` Linus Torvalds
2023-10-12 15:19 ` Nadav Amit
2023-10-12 16:33 ` Uros Bizjak
2023-10-12 16:55 ` Uros Bizjak
2023-10-12 17:10 ` Linus Torvalds
2023-10-12 17:47 ` Linus Torvalds
2023-10-12 18:01 ` Uros Bizjak
2023-10-13 9:38 ` Uros Bizjak
2023-10-13 11:53 ` Uros Bizjak
2023-10-13 16:38 ` Linus Torvalds
2023-10-12 17:52 ` Uros Bizjak
2023-11-20 9:39 ` Use %a asm operand modifier to obtain %rip-relative addressing Uros Bizjak
2023-10-12 16:56 ` [PATCH v2 -tip] x86/percpu: Use C for arch_raw_cpu_ptr() Linus Torvalds
2023-10-12 17:16 ` Linus Torvalds
2023-10-12 19:32 ` Nadav Amit
2023-10-12 19:40 ` Linus Torvalds
2023-10-16 18:52 ` Uros Bizjak
2023-10-16 19:24 ` Linus Torvalds
2023-10-16 20:35 ` Nadav Amit
2023-10-16 20:59 ` Linus Torvalds
2023-10-16 23:02 ` Linus Torvalds
2023-10-16 23:14 ` Linus Torvalds
2023-10-17 7:23 ` Nadav Amit
2023-10-17 19:00 ` Linus Torvalds
2023-10-17 19:11 ` Uros Bizjak
2023-10-17 21:05 ` Uros Bizjak
2023-10-17 21:53 ` Linus Torvalds
2023-10-17 22:06 ` Nadav Amit
2023-10-17 22:29 ` Nadav Amit
2023-10-18 7:46 ` Uros Bizjak
2023-10-18 9:04 ` Uros Bizjak
2023-10-18 10:54 ` Nadav Amit
2023-10-18 12:14 ` Uros Bizjak
2023-10-18 13:15 ` Uros Bizjak
2023-10-18 14:46 ` Nadav Amit
2023-10-18 15:17 ` Uros Bizjak
2023-10-18 16:03 ` Nadav Amit
2023-10-18 16:26 ` Linus Torvalds
2023-10-18 17:23 ` Uros Bizjak
2023-10-18 18:11 ` Linus Torvalds
2023-10-18 18:08 ` Uros Bizjak
2023-10-18 18:15 ` Linus Torvalds
2023-10-18 18:26 ` Uros Bizjak
2023-10-18 19:33 ` Uros Bizjak
2023-10-18 20:17 ` Nadav Amit
2023-10-18 20:22 ` Linus Torvalds
2023-10-18 20:34 ` Linus Torvalds
2023-10-18 20:51 ` Uros Bizjak
2023-10-18 21:09 ` Uros Bizjak
2023-10-18 21:10 ` Linus Torvalds
2023-10-18 21:40 ` Uros Bizjak
2023-10-18 22:40 ` Linus Torvalds
2023-10-18 23:06 ` Linus Torvalds
2023-10-19 7:04 ` Uros Bizjak
2023-10-19 16:59 ` Linus Torvalds
2023-10-19 17:21 ` Uros Bizjak
2023-10-19 18:06 ` Linus Torvalds
2023-10-19 18:16 ` Uros Bizjak
2023-10-19 18:49 ` Linus Torvalds
2023-10-19 19:07 ` Linus Torvalds
2023-10-20 7:57 ` Uros Bizjak
2023-10-19 21:04 ` Linus Torvalds
2023-10-19 22:39 ` Linus Torvalds
2023-10-20 8:08 ` Uros Bizjak
2023-10-19 8:44 ` Peter Zijlstra
2023-10-19 8:54 ` Peter Zijlstra
2023-10-19 17:04 ` Linus Torvalds
2023-10-19 18:13 ` Peter Zijlstra
2023-10-19 18:22 ` Linus Torvalds
2023-10-19 18:37 ` Uros Bizjak
2023-10-19 9:07 ` Peter Zijlstra
2023-10-19 9:23 ` Uros Bizjak
2023-10-18 20:42 ` Uros Bizjak
2023-10-19 16:32 ` Uros Bizjak
2023-10-19 17:08 ` Linus Torvalds
2023-10-18 18:29 ` Nadav Amit
2023-10-18 16:12 ` Linus Torvalds
2023-10-18 17:07 ` Uros Bizjak [this message]
2023-10-18 18:01 ` Linus Torvalds
2023-10-16 21:09 ` Uros Bizjak
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