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Date: Sun, 29 May 2016 21:03:56 +1000
From: Anton Blanchard <anton@samba.org>
To: "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>
Cc: benh@kernel.crashing.org, paulus@samba.org, mpe@ellerman.id.au,
 linuxppc-dev@lists.ozlabs.org, Michael Neuling <mikey@neuling.org>
Subject: Re: [PATCH V2 04/68] powerpc/mm: Use big endian page table for
 book3s 64
Message-ID: <20160529210356.66dd944e@kryten>
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Hi,

> This enables us to share the same page table code for
> both radix and hash. Radix use a hardware defined big endian
> page table

This is measurably worse (a little over 2% on POWER8) on a futex
microbenchmark:

#define _GNU_SOURCE
#include <unistd.h>
#include <sys/syscall.h>
#include <linux/futex.h>

#define ITERATIONS 10000000

#define futex(A, B, C, D, E, F)		syscall(__NR_futex, A, B, C, D, E, F)

int main(void)
{
	unsigned long i = ITERATIONS;

	while (i--) {
		unsigned int addr = 0;

		futex(&addr, FUTEX_WAKE, 1, NULL, NULL, 0);
	}

	return 0;
}

Is there any way to avoid the radix tax here?

Anton