From: Richard Henderson <richard.henderson@linaro.org>
To: "Alex Bennée" <alex.bennee@linaro.org>, qemu-devel@nongnu.org
Cc: damien.hedde@greensocs.com,
Peter Maydell <peter.maydell@linaro.org>,
"open list:ARM TCG CPUs" <qemu-arm@nongnu.org>,
luis.machado@linaro.org, alan.hayward@arm.com
Subject: Re: [PATCH v2 11/14] target/arm: default SVE length to 64 bytes for linux-user
Date: Sun, 1 Dec 2019 18:41:34 -0800 [thread overview]
Message-ID: <9362663d-6452-39aa-2a8d-1cfd853d7faa@linaro.org> (raw)
In-Reply-To: <20191130084602.10818-12-alex.bennee@linaro.org>
On 11/30/19 8:45 AM, Alex Bennée wrote:
> The Linux kernel chooses the default of 64 bytes for SVE registers on
> the basis that it is the largest size that won't grow the signal
> frame. When debugging larger sizes are also unwieldy in gdb as each
> zreg will take over a page of terminal to display.
>
> The user can of course always specify a larger size with the
> sve-max-vq property on the command line:
>
> -cpu max,sve-max-vq=16
>
> This should not make any difference to SVE enabled software as the SVE
> is of course vector length agnostic.
>
> Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> ---
> target/arm/cpu64.c | 3 +++
> 1 file changed, 3 insertions(+)
6 is the largest size that doesn't grow the signal frame.
I imagine 4 was chosen because that's the only real hw atm.
> + /* Default sve-max-vq to a reasonable numer */
> + cpu->sve_max_vq = 4;
I also agree that we should match the kernel, but this is not the right way.
Changing max vq is not the same as changing the default vq.
You should change the value of env->vfp.zcr_el[1] in arm_cpu_reset(), and the
user can increase the length with prctl(2) as they would be able to on real
hardware that would have support for longer vector lengths.
Also, I don't think you should mix this up with gdb stuff.
r~
next prev parent reply other threads:[~2019-12-02 2:42 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-11-30 8:45 [PATCH v2 00/14] gdbstub refactor and SVE support Alex Bennée
2019-11-30 8:45 ` [PATCH v2 01/14] gdbstub: make GDBState static and have common init function Alex Bennée
2019-12-02 2:14 ` Richard Henderson
2019-12-02 14:35 ` Damien Hedde
2019-11-30 8:45 ` [PATCH v2 02/14] gdbstub: stop passing GDBState * around and use global Alex Bennée
2019-12-02 2:16 ` Richard Henderson
2019-12-02 15:25 ` Damien Hedde
2019-11-30 8:45 ` [PATCH v2 03/14] gdbstub: move str_buf to GDBState and use GString Alex Bennée
2019-12-02 15:26 ` Damien Hedde
2019-12-03 12:49 ` Damien Hedde
2019-11-30 8:45 ` [PATCH v2 04/14] gdbstub: move mem_buf to GDBState and use GByteArray Alex Bennée
2019-12-03 11:11 ` Damien Hedde
2019-11-30 8:45 ` [PATCH v2 05/14] gdbstub: add helper for 128 bit registers Alex Bennée
2019-12-01 20:02 ` Philippe Mathieu-Daudé
2019-12-02 2:19 ` Richard Henderson
2019-11-30 8:45 ` [PATCH v2 06/14] target/arm: use gdb_get_reg helpers Alex Bennée
2019-12-01 20:05 ` Philippe Mathieu-Daudé
2019-12-02 10:05 ` Alan Hayward
2019-12-05 17:58 ` Alex Bennée
2019-12-02 2:20 ` Richard Henderson
2019-11-30 8:45 ` [PATCH v2 07/14] target/m68k: " Alex Bennée
2019-11-30 10:58 ` Laurent Vivier
2019-11-30 8:45 ` [PATCH v2 08/14] gdbstub: extend GByteArray to read register helpers Alex Bennée
2019-12-02 2:24 ` Richard Henderson
2019-11-30 8:45 ` [PATCH v2 09/14] target/arm: prepare for multiple dynamic XMLs Alex Bennée
2019-12-02 18:26 ` Richard Henderson
2019-11-30 8:45 ` [PATCH v2 10/14] target/arm: explicitly encode regnum in our XML Alex Bennée
2019-11-30 8:45 ` [PATCH v2 11/14] target/arm: default SVE length to 64 bytes for linux-user Alex Bennée
2019-12-02 2:41 ` Richard Henderson [this message]
2019-12-05 17:31 ` Alex Bennée
2019-12-05 19:36 ` Richard Henderson
2019-12-06 14:52 ` Alex Bennée
2019-11-30 8:46 ` [PATCH v2 12/14] target/arm: generate xml description of our SVE registers Alex Bennée
2019-12-02 18:44 ` Richard Henderson
2019-11-30 8:46 ` [PATCH v2 13/14] tests/guest-debug: add a simple test runner Alex Bennée
2019-12-02 18:50 ` Richard Henderson
2019-11-30 8:46 ` [PATCH v2 14/14] tests/tcg: add a gdbstub testcase for SVE registers Alex Bennée
2019-11-30 9:33 ` [PATCH v2 00/14] gdbstub refactor and SVE support no-reply
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