Re: [PATCH v4 2/7] um: enable the use of optimized xor routines in UML

Anton Ivanov
2020-12-11T21:57:20Z

On 11/12/2020 20:07, Johannes Berg wrote:
>> +++ b/arch/um/include/asm/fpu/api.h
>> @@ -0,0 +1,14 @@
>> +/* SPDX-License-Identifier: GPL-2.0-or-later */
>> +#ifndef _ASM_UM_FPU_API_H
>> +#define _ASM_UM_FPU_API_H
>> +
>> +/* Copyright (c) 2020 Cambridge Greys Ltd
>> + * Copyright (c) 2020 Red Hat Inc.
>> + * A set of "dummy" defines to allow the direct inclusion
>> + * of x86 optimized copy, xor, etc routines into the
>> + * UML code tree. */
>> +
>> +#define kernel_fpu_begin() (void)0
>> +#define kernel_fpu_end() (void)0
> I think I would prefer those to be static inlines, but YMMV.
>
> johannes
>
>> diff --git a/arch/um/include/asm/xor-x86.h b/arch/um/include/asm/xor-x86.h
>> new file mode 120000
>> index 000000000000..beff7de6890d
>> --- /dev/null
>> +++ b/arch/um/include/asm/xor-x86.h
>> @@ -0,0 +1 @@
>> +../../../x86/include/asm/xor.h
> Do these really need to be symlinks? Last I looked, it seemed that
> arch/x86/include/asm/ is actually in the include path?

It is included, but it is included quite far down the list.

We pick up a few things out of there, but if we leave them "as is" they
all default to their least optimized versions. The results clearly
demonstrate that too - 30% difference on 64 bit and > 100% on 32 bit.

This is because we do not perform alternatives substitution. Our
"alternatives" processing function in the UML startup is a noop.

My idea was to override that to the extent possible and get whatever
mileage is possible without that.

I can give it a try to see how it looks if I use the x86 feature table
and other bits which are picked up from there, but working with that is
like pulling teeth without anaesthetic.

On the positive side this means that we can copy the alternatives code
on x86.

I can give it another go. I tried early on and it was a bit painful.

A.

>
>> --- a/arch/um/include/asm/xor.h
>> +++ b/arch/um/include/asm/xor.h
>> @@ -1,7 +1,22 @@
>> /* SPDX-License-Identifier: GPL-2.0 */
>> -#include <asm-generic/xor.h>
>> +#ifndef _ASM_UM_XOR_H
>> +#define _ASM_UM_XOR_H
>> +
>> +#ifdef CONFIG_64BIT
>> +#undef CONFIG_X86_32
>> +#else
>> +#define CONFIG_X86_32 1
>> +#endif
>> +
>> +#include <asm/cpufeature.h>
>> +#include <asm/xor-x86.h>
> and thus this could just be
>
> #include_next <asm/xor.h>
>
> without the symlink?
>
>> diff --git a/arch/um/include/asm/xor_32.h b/arch/um/include/asm/xor_32.h
>> new file mode 120000
>> index 000000000000..8a0894e996d7
>> --- /dev/null
>> +++ b/arch/um/include/asm/xor_32.h
>
> And the others don't exist in um anyway, so probably aren't needed?
>
> But maybe I'm confused about the include path, I didn't double-check
> now.
>
> johannes
>
>
>
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>

--
Anton R. Ivanov
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