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Re: [Qemu-arm] [PATCH 04/11] hw/arm/aspeed: add a 'mmio-exec' property t

From: Peter Maydell
Subject: Re: [Qemu-arm] [PATCH 04/11] hw/arm/aspeed: add a 'mmio-exec' property to boot from the FMC flash module
Date: Mon, 24 Sep 2018 12:41:04 +0100

On 19 September 2018 at 11:19, Cédric Le Goater <address@hidden> wrote:
> These are the number of read operations done on the flash memory region :
>     922478 ~ 3.5 MBytes   OpenBMC U-Boot
>   20569977 ~ 80  MBytes   Mainline U-Boot
> So we are trashing the TBs I would say. Is there a way to increase the
> TB size ? or some other TB parameter ? Is that directly linked to the
> instruction cache size ?

Well, execution direct from MMIO means we read each instruction
as we execute it -- there's no caching of TBs. (We generate a
temporary TB with a single insn and throw it away after executing
from it.) This is because we can't be sure that we would get the
same data value the next time we read from the address.
So we definitely expect things to go slower -- I'm just a little
surprised that we spend so much time executing from flash devices
that aren't in "romd" mode.

-- PMM

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