Subject: Re: [PATCH net-next 1/2] tools: add missing infrastructure for building ptr_ring.h

From: "Michael S. Tsirkin" <[email-masked]>
Date: Sat, 17 Jul 2021 22:09:13 -0400

On Tue, Jul 06, 2021 at 10:04:02AM +0800, Yunsheng Lin wrote:
> On 2021/7/6 2:39, Michael S. Tsirkin wrote:
> > On Mon, Jul 05, 2021 at 11:57:34AM +0800, Yunsheng Lin wrote:
> >> In order to build ptr_ring.h in userspace, the cacheline
> >> aligning, cpu_relax() and slab related infrastructure is
> >> needed, so add them in this patch.
> >>
> >> As L1_CACHE_BYTES may be different for different arch, which
> >> is mostly defined in include/generated/autoconf.h, so user may
> >> need to do "make defconfig" before building a tool using the
> >> API in linux/cache.h.
> >>
> >> Also "linux/lockdep.h" is not added in "tools/include" yet,
> >> so remove it in "linux/spinlock.h", and the only place using
> >> "linux/spinlock.h" is tools/testing/radix-tree, removing that
> >> does not break radix-tree testing.
> >>
> >> Signed-off-by: Yunsheng Lin <[email-masked]>
> > 
> > This is hard to review.
> > Try to split this please. Functional changes separate from
> > merely moving code around.
> 
> Sure.
> 
> > 
> > 
> >> ---
> >>  tools/include/asm/cache.h          | 56 ++++++++++++++++++++++++
> >>  tools/include/asm/processor.h      | 36 ++++++++++++++++
> >>  tools/include/generated/autoconf.h |  1 +
> >>  tools/include/linux/align.h        | 15 +++++++
> >>  tools/include/linux/cache.h        | 87 ++++++++++++++++++++++++++++++++++++++
> >>  tools/include/linux/gfp.h          |  4 ++
> >>  tools/include/linux/slab.h         | 46 ++++++++++++++++++++
> >>  tools/include/linux/spinlock.h     |  2 -
> >>  8 files changed, 245 insertions(+), 2 deletions(-)
> >>  create mode 100644 tools/include/asm/cache.h
> >>  create mode 100644 tools/include/asm/processor.h
> >>  create mode 100644 tools/include/generated/autoconf.h
> >>  create mode 100644 tools/include/linux/align.h
> >>  create mode 100644 tools/include/linux/cache.h
> >>  create mode 100644 tools/include/linux/slab.h
> >>
> >> diff --git a/tools/include/asm/cache.h b/tools/include/asm/cache.h
> >> new file mode 100644
> >> index 0000000..071e310
> >> --- /dev/null
> >> +++ b/tools/include/asm/cache.h
> >> @@ -0,0 +1,56 @@
> >> +/* SPDX-License-Identifier: GPL-2.0 */
> >> +
> >> +#ifndef __TOOLS_LINUX_ASM_CACHE_H
> >> +#define __TOOLS_LINUX_ASM_CACHE_H
> >> +
> >> +#include <generated/autoconf.h>
> >> +
> >> +#if defined(__i386__) || defined(__x86_64__)
> >> +#define L1_CACHE_SHIFT	(CONFIG_X86_L1_CACHE_SHIFT)
> >> +#elif defined(__arm__)
> >> +#define L1_CACHE_SHIFT	(CONFIG_ARM_L1_CACHE_SHIFT)
> >> +#elif defined(__aarch64__)
> >> +#define L1_CACHE_SHIFT	(6)
> >> +#elif defined(__powerpc__)
> >> +
> >> +/* bytes per L1 cache line */
> >> +#if defined(CONFIG_PPC_8xx)
> >> +#define L1_CACHE_SHIFT	4
> >> +#elif defined(CONFIG_PPC_E500MC)
> >> +#define L1_CACHE_SHIFT	6
> >> +#elif defined(CONFIG_PPC32)
> >> +#if defined(CONFIG_PPC_47x)
> >> +#define L1_CACHE_SHIFT	7
> >> +#else
> >> +#define L1_CACHE_SHIFT	5
> >> +#endif
> >> +#else /* CONFIG_PPC64 */
> >> +#define L1_CACHE_SHIFT	7
> >> +#endif
> >> +
> >> +#elif defined(__sparc__)
> >> +#define L1_CACHE_SHIFT 5
> >> +#elif defined(__alpha__)
> >> +
> >> +#if defined(CONFIG_ALPHA_GENERIC) || defined(CONFIG_ALPHA_EV6)
> >> +#define L1_CACHE_SHIFT	6
> >> +#else
> >> +/* Both EV4 and EV5 are write-through, read-allocate,
> >> +   direct-mapped, physical.
> >> +*/
> >> +#define L1_CACHE_SHIFT	5
> >> +#endif
> >> +
> >> +#elif defined(__mips__)
> >> +#define L1_CACHE_SHIFT	CONFIG_MIPS_L1_CACHE_SHIFT
> >> +#elif defined(__ia64__)
> >> +#define L1_CACHE_SHIFT	CONFIG_IA64_L1_CACHE_SHIFT
> >> +#elif defined(__nds32__)
> >> +#define L1_CACHE_SHIFT	5
> >> +#else
> >> +#define L1_CACHE_SHIFT	5
> >> +#endif
> >> +
> >> +#define L1_CACHE_BYTES	(1 << L1_CACHE_SHIFT)
> >> +
> >> +#endif
> >> diff --git a/tools/include/asm/processor.h b/tools/include/asm/processor.h
> >> new file mode 100644
> >> index 0000000..3198ad6
> >> --- /dev/null
> >> +++ b/tools/include/asm/processor.h
> >> @@ -0,0 +1,36 @@
> >> +/* SPDX-License-Identifier: GPL-2.0 */
> >> +
> >> +#ifndef __TOOLS_LINUX_ASM_PROCESSOR_H
> >> +#define __TOOLS_LINUX_ASM_PROCESSOR_H
> >> +
> >> +#include <pthread.h>
> >> +
> >> +#if defined(__i386__) || defined(__x86_64__)
> >> +#include "../../arch/x86/include/asm/vdso/processor.h"
> >> +#elif defined(__arm__)
> >> +#include "../../arch/arm/include/asm/vdso/processor.h"
> >> +#elif defined(__aarch64__)
> >> +#include "../../arch/arm64/include/asm/vdso/processor.h"
> >> +#elif defined(__powerpc__)
> >> +#include "../../arch/powerpc/include/vdso/processor.h"
> >> +#elif defined(__s390__)
> >> +#include "../../arch/s390/include/vdso/processor.h"
> >> +#elif defined(__sh__)
> >> +#include "../../arch/sh/include/asm/processor.h"
> >> +#elif defined(__sparc__)
> >> +#include "../../arch/sparc/include/asm/processor.h"
> >> +#elif defined(__alpha__)
> >> +#include "../../arch/alpha/include/asm/processor.h"
> >> +#elif defined(__mips__)
> >> +#include "../../arch/mips/include/asm/vdso/processor.h"
> >> +#elif defined(__ia64__)
> >> +#include "../../arch/ia64/include/asm/processor.h"
> >> +#elif defined(__xtensa__)
> >> +#include "../../arch/xtensa/include/asm/processor.h"
> >> +#elif defined(__nds32__)
> >> +#include "../../arch/nds32/include/asm/processor.h"
> >> +#else
> >> +#define cpu_relax()	sched_yield()
> > 
> > Does this have a chance to work outside of kernel?
> 
> I am not sure I understand what you meant here.
> sched_yield() is a pthread API, so it should work in the
> user space.
> And it allow the rigntest to compile when it is built on
> the arch which is not handled as above.

It might compile but is likely too heavy to behave
reasonably.

Also, given you did not actually test it I don't
think you should add such arch code.
Note you broke at least s390 here:
../../arch/s390/include/vdso/processor.h
does not actually exist. Where these headers
do exit they tend to include lots of code which won't
build out of kernel.

All this is just for cpu_relax - open coding that seems way easier.

> > 
> >> +#endif
> > 
> > did you actually test or even test build all these arches?
> > Not sure we need to bother with hacks like these.
> 
> Only x86_64 and arm64 arches have been built and tested.

In that case I think you should not add code that you
have not even built let alone tested.

> This is added referring the tools/include/asm/barrier.h.
> 
> > 
> > 
> >> +