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.
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).
Fixes: 8e20fc391711 ("serial_core: Move sysrq functions from header file")
Cc: Dmitry Safonov <[email protected]>
Signed-off-by: Johan Hovold <[email protected]>
---
drivers/tty/serial/serial_core.c | 99 +----------------------------
include/linux/serial_core.h | 103 +++++++++++++++++++++++++++++--
2 files changed, 100 insertions(+), 102 deletions(-)
diff --git a/drivers/tty/serial/serial_core.c b/drivers/tty/serial/serial_core.c
index 296b9f6fa9cd..3706f31b0c37 100644
--- a/drivers/tty/serial/serial_core.c
+++ b/drivers/tty/serial/serial_core.c
@@ -41,8 +41,6 @@ static struct lock_class_key port_lock_key;
#define HIGH_BITS_OFFSET ((sizeof(long)-sizeof(int))*8)
-#define SYSRQ_TIMEOUT (HZ * 5)
-
static void uart_change_speed(struct tty_struct *tty, struct uart_state *state,
struct ktermios *old_termios);
static void uart_wait_until_sent(struct tty_struct *tty, int timeout);
@@ -3163,7 +3161,7 @@ static DECLARE_WORK(sysrq_enable_work, uart_sysrq_on);
* Returns false if @ch is out of enabling sequence and should be
* handled some other way, true if @ch was consumed.
*/
-static bool uart_try_toggle_sysrq(struct uart_port *port, unsigned int ch)
+bool uart_try_toggle_sysrq(struct uart_port *port, unsigned int ch)
{
int sysrq_toggle_seq_len = strlen(sysrq_toggle_seq);
@@ -3186,102 +3184,9 @@ static bool uart_try_toggle_sysrq(struct uart_port *port, unsigned int ch)
port->sysrq = 0;
return true;
}
-#else
-static inline bool uart_try_toggle_sysrq(struct uart_port *port, unsigned int ch)
-{
- return false;
-}
+EXPORT_SYMBOL_GPL(uart_try_toggle_sysrq);
#endif
-int uart_handle_sysrq_char(struct uart_port *port, unsigned int ch)
-{
- if (!IS_ENABLED(CONFIG_MAGIC_SYSRQ_SERIAL))
- return 0;
-
- if (!port->has_sysrq || !port->sysrq)
- return 0;
-
- if (ch && time_before(jiffies, port->sysrq)) {
- if (sysrq_mask()) {
- handle_sysrq(ch);
- port->sysrq = 0;
- return 1;
- }
- if (uart_try_toggle_sysrq(port, ch))
- return 1;
- }
- port->sysrq = 0;
-
- return 0;
-}
-EXPORT_SYMBOL_GPL(uart_handle_sysrq_char);
-
-int uart_prepare_sysrq_char(struct uart_port *port, unsigned int ch)
-{
- if (!IS_ENABLED(CONFIG_MAGIC_SYSRQ_SERIAL))
- return 0;
-
- if (!port->has_sysrq || !port->sysrq)
- return 0;
-
- if (ch && time_before(jiffies, port->sysrq)) {
- if (sysrq_mask()) {
- port->sysrq_ch = ch;
- port->sysrq = 0;
- return 1;
- }
- if (uart_try_toggle_sysrq(port, ch))
- return 1;
- }
- port->sysrq = 0;
-
- return 0;
-}
-EXPORT_SYMBOL_GPL(uart_prepare_sysrq_char);
-
-void uart_unlock_and_check_sysrq(struct uart_port *port, unsigned long irqflags)
-{
- int sysrq_ch;
-
- if (!port->has_sysrq) {
- spin_unlock_irqrestore(&port->lock, irqflags);
- return;
- }
-
- sysrq_ch = port->sysrq_ch;
- port->sysrq_ch = 0;
-
- spin_unlock_irqrestore(&port->lock, irqflags);
-
- if (sysrq_ch)
- handle_sysrq(sysrq_ch);
-}
-EXPORT_SYMBOL_GPL(uart_unlock_and_check_sysrq);
-
-/*
- * We do the SysRQ and SAK checking like this...
- */
-int uart_handle_break(struct uart_port *port)
-{
- struct uart_state *state = port->state;
-
- if (port->handle_break)
- port->handle_break(port);
-
- if (port->has_sysrq && uart_console(port)) {
- if (!port->sysrq) {
- port->sysrq = jiffies + SYSRQ_TIMEOUT;
- return 1;
- }
- port->sysrq = 0;
- }
-
- if (port->flags & UPF_SAK)
- do_SAK(state->port.tty);
- return 0;
-}
-EXPORT_SYMBOL_GPL(uart_handle_break);
-
EXPORT_SYMBOL(uart_write_wakeup);
EXPORT_SYMBOL(uart_register_driver);
EXPORT_SYMBOL(uart_unregister_driver);
diff --git a/include/linux/serial_core.h b/include/linux/serial_core.h
index ef4921ddbe97..03fa7b967103 100644
--- a/include/linux/serial_core.h
+++ b/include/linux/serial_core.h
@@ -462,11 +462,104 @@ extern void uart_handle_cts_change(struct uart_port *uport,
extern void uart_insert_char(struct uart_port *port, unsigned int status,
unsigned int overrun, unsigned int ch, unsigned int flag);
-extern int uart_handle_sysrq_char(struct uart_port *port, unsigned int ch);
-extern int uart_prepare_sysrq_char(struct uart_port *port, unsigned int ch);
-extern void uart_unlock_and_check_sysrq(struct uart_port *port,
- unsigned long irqflags);
-extern int uart_handle_break(struct uart_port *port);
+#ifdef CONFIG_MAGIC_SYSRQ_SERIAL
+#define SYSRQ_TIMEOUT (HZ * 5)
+
+bool uart_try_toggle_sysrq(struct uart_port *port, unsigned int ch);
+
+static inline int uart_handle_sysrq_char(struct uart_port *port, unsigned int ch)
+{
+ if (!port->has_sysrq || !port->sysrq)
+ return 0;
+
+ if (ch && time_before(jiffies, port->sysrq)) {
+ if (sysrq_mask()) {
+ handle_sysrq(ch);
+ port->sysrq = 0;
+ return 1;
+ }
+ if (uart_try_toggle_sysrq(port, ch))
+ return 1;
+ }
+ port->sysrq = 0;
+
+ return 0;
+}
+
+static inline int uart_prepare_sysrq_char(struct uart_port *port, unsigned int ch)
+{
+ if (!port->has_sysrq || !port->sysrq)
+ return 0;
+
+ if (ch && time_before(jiffies, port->sysrq)) {
+ if (sysrq_mask()) {
+ port->sysrq_ch = ch;
+ port->sysrq = 0;
+ return 1;
+ }
+ if (uart_try_toggle_sysrq(port, ch))
+ return 1;
+ }
+ port->sysrq = 0;
+
+ return 0;
+}
+
+static inline void uart_unlock_and_check_sysrq(struct uart_port *port, unsigned long irqflags)
+{
+ int sysrq_ch;
+
+ if (!port->has_sysrq) {
+ spin_unlock_irqrestore(&port->lock, irqflags);
+ return;
+ }
+
+ sysrq_ch = port->sysrq_ch;
+ port->sysrq_ch = 0;
+
+ spin_unlock_irqrestore(&port->lock, irqflags);
+
+ if (sysrq_ch)
+ handle_sysrq(sysrq_ch);
+}
+#else /* CONFIG_MAGIC_SYSRQ_SERIAL */
+static inline int uart_handle_sysrq_char(struct uart_port *port, unsigned int ch)
+{
+ return 0;
+}
+static inline int uart_prepare_sysrq_char(struct uart_port *port, unsigned int ch)
+{
+ return 0;
+}
+static inline void uart_unlock_and_check_sysrq(struct uart_port *port, unsigned long irqflags)
+{
+ spin_unlock_irqrestore(&port->lock, irqflags);
+}
+#endif /* CONFIG_MAGIC_SYSRQ_SERIAL */
+
+/*
+ * We do the SysRQ and SAK checking like this...
+ */
+static inline int uart_handle_break(struct uart_port *port)
+{
+ struct uart_state *state = port->state;
+
+ if (port->handle_break)
+ port->handle_break(port);
+
+#ifdef CONFIG_MAGIC_SYSRQ_SERIAL
+ if (port->has_sysrq && uart_console(port)) {
+ if (!port->sysrq) {
+ port->sysrq = jiffies + SYSRQ_TIMEOUT;
+ return 1;
+ }
+ port->sysrq = 0;
+ }
+#endif
+ if (port->flags & UPF_SAK)
+ do_SAK(state->port.tty);
+ return 0;
+}
/*
* UART_ENABLE_MS - determine if port should enable modem status irqs
--
2.26.2
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).
If one function call actually matters here, than should
uart_insert_char() also go into header?
I see quite common pattern in drivers:
: if (!uart_handle_sysrq_char(&up->port, ch))
: uart_insert_char(&up->port, byte, 0, ch, TTY_NORMAL);
Don't misunderstand me, but I would prefer keeping headers cleaner
without realization details with the exception if function calls
actually hurts the performance.
Probably, a comment like
/*
* Keeping these functions in the header improves performance by X% on
* YYY platform by letting the compiler inline them.
*/
would also help.
Thanks for working on this,
Dmitry
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
On 6/12/20 4:29 PM, Johan Hovold wrote:
> 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.
I think the number justifies moving them back to header.
>
>> 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.
Fair enough
> The point is that we don't want a rarely used debugging feature to incur
> unnecessary additional overhead that can easily be avoided.
Well, it wasn't related to the debug feature, rather I wanted to cleanup
the header from a bit over-grown functions those have realization
details. And couldn't foresee that a function call would matter for some
setup.
Thanks,
Dmitry
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.
>
> 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).
>
> Fixes: 8e20fc391711 ("serial_core: Move sysrq functions from header file")
> Cc: Dmitry Safonov <[email protected]>
> Signed-off-by: Johan Hovold <[email protected]>
Thanks for sending and the numbers, it's a bit pity that we need to move
them back to the header, but as it matters for your setup,
Reviewed-by: Dmitry Safonov <[email protected]>
Thanks,
Dmitry