From: Johan Hovold <johan@kernel.org>
To: Dmitry Safonov <0x7f454c46@gmail.com>
Cc: Johan Hovold <johan@kernel.org>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Jiri Slaby <jslaby@suse.com>,
Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
linux-serial@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH v2 2/3] serial: core: fix sysrq overhead regression
Date: Fri, 12 Jun 2020 17:29:21 +0200 [thread overview]
Message-ID: <20200612152921.GP19480@localhost> (raw)
In-Reply-To: <19008afb-bfbb-35e2-3bd5-e7fd1b7355cc@gmail.com>
On Wed, Jun 10, 2020 at 05:24:57PM +0100, Dmitry Safonov wrote:
> Hi Johan,
>
> On 6/10/20 4:22 PM, Johan Hovold wrote:
> > Commit 8e20fc391711 ("serial_core: Move sysrq functions from header
> > file") converted the inline sysrq helpers to exported functions which
> > are now called for every received character, interrupt and break signal
> > also on systems without CONFIG_MAGIC_SYSRQ_SERIAL instead of being
> > optimised away by the compiler.
>
> The part with ifdeffing looks good to me.
>
> > Inlining these helpers again also avoids the function call overhead when
> > CONFIG_MAGIC_SYSRQ_SERIAL is enabled (e.g. when the port is not used as
> > a console).
>
> But this one, coul you add measures? (it will also help to understand if
> it's a stable material).
Interrupt processing takes 2-3% longer without the inlining with
8250_omap on a beagleboard for example.
> If one function call actually matters here, than should
> uart_insert_char() also go into header?
Good question, it actually was originally intended to be inlined as all
other per-character processing. Separate discussion though.
The point is that we don't want a rarely used debugging feature to incur
unnecessary additional overhead that can easily be avoided.
Johan
next prev parent reply other threads:[~2020-06-12 15:29 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-06-10 15:22 [PATCH v2 0/3] serial: core: fix up sysrq regressions Johan Hovold
2020-06-10 15:22 ` [PATCH v2 1/3] Revert "serial: core: Refactor uart_unlock_and_check_sysrq()" Johan Hovold
2020-06-10 15:22 ` [PATCH v2 2/3] serial: core: fix sysrq overhead regression Johan Hovold
2020-06-10 16:24 ` Dmitry Safonov
2020-06-12 15:29 ` Johan Hovold [this message]
2020-06-12 15:42 ` Dmitry Safonov
2020-06-12 15:52 ` Dmitry Safonov
2020-06-10 15:22 ` [PATCH v2 3/3] serial: core: drop redundant sysrq checks Johan Hovold
2020-06-12 15:55 ` Dmitry Safonov
2020-06-10 16:21 ` [PATCH v2 0/3] serial: core: fix up sysrq regressions Andy Shevchenko
2020-06-12 15:31 ` Johan Hovold
2020-06-27 14:16 ` Greg Kroah-Hartman
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