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Date: Fri, 22 Jul 2016 00:34:06 +0000
From: "Zheng, Lv" <lv.zheng@...el.com>
To: "Rafael J. Wysocki" <rjw@...ysocki.net>
CC: "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
"Brown, Len" <len.brown@...el.com>, Lv Zheng <zetalog@...il.com>,
"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>
Subject: RE: [PATCH v2 1/2] ACPI / debugger: Add kernel flushing support
Hi,
> From: linux-acpi-owner@...r.kernel.org [mailto:linux-acpi-
> owner@...r.kernel.org] On Behalf Of Rafael J. Wysocki
> Subject: Re: [PATCH v2 1/2] ACPI / debugger: Add kernel flushing support
>
> On Tuesday, July 19, 2016 06:00:39 PM Lv Zheng wrote:
> > This patch adds debugger log flushing support in kernel via .ioctl()
> > callback. The in-kernel flushing is more efficient, because it reduces
> > useless log IOs by bypassing log user_read/kern_write during the flush
> > period.
> >
> > Signed-off-by: Lv Zheng <lv.zheng@...el.com>
>
> Overall, this is an optimization, right?
>
> So is adding a new IOCTL really worth it?
[Lv Zheng]
I was thinking I could use fsync.
But most of the kernel drivers implement fsync to flush data to the storage device.
And tty uses IOCTL to flush the input/output streams.
So I changed my mind to use ioctl.
>
> > ---
> > drivers/acpi/acpi_dbg.c | 98
> +++++++++++++++++++++++++++++++++++++++++--
> > include/linux/acpi-ioctls.h | 21 ++++++++++
> > 2 files changed, 115 insertions(+), 4 deletions(-)
> > create mode 100644 include/linux/acpi-ioctls.h
> >
> > diff --git a/drivers/acpi/acpi_dbg.c b/drivers/acpi/acpi_dbg.c
> > index dee8692..6ac1388 100644
> > --- a/drivers/acpi/acpi_dbg.c
> > +++ b/drivers/acpi/acpi_dbg.c
> > @@ -22,6 +22,7 @@
> > #include <linux/debugfs.h>
> > #include <linux/circ_buf.h>
> > #include <linux/acpi.h>
> > +#include <linux/acpi-ioctls.h>
>
> That should go into the uapi directory at least.
[Lv Zheng]
OK.
I'll check it.
>
> > #include "internal.h"
> >
> > #define ACPI_AML_BUF_ALIGN (sizeof (acpi_size))
> > @@ -46,6 +47,8 @@
> > #define ACPI_AML_KERN (ACPI_AML_IN_KERN |
> ACPI_AML_OUT_KERN)
> > #define ACPI_AML_BUSY (ACPI_AML_USER |
> ACPI_AML_KERN)
> > #define ACPI_AML_OPEN (ACPI_AML_OPENED |
> ACPI_AML_CLOSED)
> > +#define ACPI_AML_FLUSHING_LOG 0x0040 /* flushing log
> output */
> > +#define ACPI_AML_WAITING_CMD 0x0080 /* waiting for cmd input */
> >
> > struct acpi_aml_io {
> > wait_queue_head_t wait;
> > @@ -120,6 +123,20 @@ static inline bool __acpi_aml_busy(void)
> > return false;
> > }
> >
> > +static inline bool __acpi_aml_waiting_cmd(void)
> > +{
> > + if (acpi_aml_io.flags & ACPI_AML_WAITING_CMD)
> > + return true;
> > + return false;
>
> Oh well.
>
> What about
[Lv Zheng]
OK.
>
> return !!(acpi_aml_io.flags & ACPI_AML_WAITING_CMD);
>
> > +}
> > +
> > +static inline bool __acpi_aml_flushing_log(void)
> > +{
> > + if (acpi_aml_io.flags & ACPI_AML_FLUSHING_LOG)
> > + return true;
> > + return false;
>
> And analogously here?
[Lv Zheng]
OK.
>
> > +}
> > +
> > static inline bool __acpi_aml_opened(void)
> > {
> > if (acpi_aml_io.flags & ACPI_AML_OPEN)
> > @@ -152,6 +169,26 @@ static bool acpi_aml_busy(void)
> > return ret;
> > }
> >
> > +static inline bool acpi_aml_waiting_cmd(void)
> > +{
> > + bool ret;
> > +
> > + mutex_lock(&acpi_aml_io.lock);
> > + ret = __acpi_aml_waiting_cmd();
> > + mutex_unlock(&acpi_aml_io.lock);
> > + return ret;
> > +}
> > +
> > +static inline bool acpi_aml_flushing_log(void)
> > +{
> > + bool ret;
> > +
> > + mutex_lock(&acpi_aml_io.lock);
> > + ret = __acpi_aml_flushing_log();
> > + mutex_unlock(&acpi_aml_io.lock);
> > + return ret;
> > +}
> > +
> > static bool acpi_aml_used(void)
> > {
> > bool ret;
> > @@ -183,7 +220,8 @@ static bool acpi_aml_kern_writable(void)
> >
> > mutex_lock(&acpi_aml_io.lock);
> > ret = !__acpi_aml_access_ok(ACPI_AML_OUT_KERN) ||
> > - __acpi_aml_writable(&acpi_aml_io.out_crc,
> ACPI_AML_OUT_KERN);
> > + __acpi_aml_writable(&acpi_aml_io.out_crc,
> ACPI_AML_OUT_KERN) ||
> > + __acpi_aml_flushing_log();
> > mutex_unlock(&acpi_aml_io.lock);
> > return ret;
> > }
> > @@ -264,6 +302,9 @@ static int acpi_aml_write_kern(const char *buf,
> int len)
> > int n;
> > char *p;
> >
> > + if (acpi_aml_flushing_log())
> > + return len;
> > +
> > ret = acpi_aml_lock_write(crc, ACPI_AML_OUT_KERN);
> > if (ret < 0)
> > return ret;
> > @@ -458,9 +499,18 @@ static int acpi_aml_wait_command_ready(bool
> single_step,
> > else
> > acpi_os_printf("\n%1c ",
> ACPI_DEBUGGER_COMMAND_PROMPT);
> >
> > + mutex_lock(&acpi_aml_io.lock);
> > + acpi_aml_io.flags |= ACPI_AML_WAITING_CMD;
> > + wake_up_interruptible(&acpi_aml_io.wait);
> > + mutex_unlock(&acpi_aml_io.lock);
> > +
> > status = acpi_os_get_line(buffer, length, NULL);
> > if (ACPI_FAILURE(status))
> > return -EINVAL;
> > +
> > + mutex_lock(&acpi_aml_io.lock);
> > + acpi_aml_io.flags &= ~ACPI_AML_WAITING_CMD;
> > + mutex_unlock(&acpi_aml_io.lock);
> > return 0;
> > }
> >
> > @@ -593,9 +643,11 @@ static int acpi_aml_read_user(char __user *buf,
> int len)
> > smp_rmb();
> > p = &crc->buf[crc->tail];
> > n = min(len, circ_count_to_end(crc));
> > - if (copy_to_user(buf, p, n)) {
> > - ret = -EFAULT;
> > - goto out;
> > + if (!acpi_aml_flushing_log()) {
> > + if (copy_to_user(buf, p, n)) {
> > + ret = -EFAULT;
> > + goto out;
> > + }
> > }
> > /* sync tail after removing logs */
> > smp_mb();
> > @@ -731,10 +783,48 @@ static unsigned int acpi_aml_poll(struct file
> *file, poll_table *wait)
> > return masks;
> > }
> >
> > +static int acpi_aml_flush(void)
> > +{
> > + int ret;
> > +
> > + /*
> > + * Discard output buffer and put the driver into a state waiting
> > + * for the new user input.
> > + */
> > + mutex_lock(&acpi_aml_io.lock);
> > + acpi_aml_io.flags |= ACPI_AML_FLUSHING_LOG;
> > + mutex_unlock(&acpi_aml_io.lock);
> > +
> > + ret = wait_event_interruptible(acpi_aml_io.wait,
> > + acpi_aml_waiting_cmd());
> > + (void)acpi_aml_read_user(NULL, ACPI_AML_BUF_SIZE);
> > +
> > + mutex_lock(&acpi_aml_io.lock);
> > + acpi_aml_io.flags &= ~ACPI_AML_FLUSHING_LOG;
> > + mutex_unlock(&acpi_aml_io.lock);
> > + return ret;
> > +}
> > +
> > +static long acpi_aml_ioctl(struct file *file,
> > + unsigned int cmd, unsigned long arg)
> > +{
> > + long ret = -EINVAL;
> > +
> > + switch (cmd) {
> > + case ACPI_IOCTL_DEBUGGER_FLUSH:
> > + ret = acpi_aml_flush();
> > + break;
> > + default:
> > + break;
> > + }
> > + return ret;
>
> return cmd == ACPI_IOCTL_DEBUGGER_FLUSH ? acpi_aml_flush() :
> -EINVAL;
[Lv Zheng]
OK.
>
> > +}
> > +
> > static const struct file_operations acpi_aml_operations = {
> > .read = acpi_aml_read,
> > .write = acpi_aml_write,
> > .poll = acpi_aml_poll,
> > + .unlocked_ioctl = acpi_aml_ioctl,
> > .open = acpi_aml_open,
> > .release = acpi_aml_release,
> > .llseek = generic_file_llseek,
> > diff --git a/include/linux/acpi-ioctls.h b/include/linux/acpi-ioctls.h
> > new file mode 100644
> > index 0000000..56b8170
> > --- /dev/null
> > +++ b/include/linux/acpi-ioctls.h
>
> include/uapi/linux/
[Lv Zheng]
OK.
>
> > @@ -0,0 +1,21 @@
> > +/*
> > + * ACPI IOCTL collections
> > + *
> > + * Copyright (C) 2016, Intel Corporation
> > + * Authors: Lv Zheng <lv.zheng@...el.com>
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + */
> > +
> > +#ifndef _LINUX_ACPI_IOCTLS_H
> > +#define _LINUX_ACPI_IOCTLS_H
> > +
> > +#include <linux/ioctl.h>
> > +
> > +#define ACPI_IOCTL_IDENT 'a'
> > +
> > +#define ACPI_IOCTL_DEBUGGER_FLUSH _IO(ACPI_IOCTL_IDENT,
> 0x80)
> > +
> > +#endif /* _LINUX_ACPI_IOCTLS_H */
> >
>
> Plus patches that change the ABI should be CCed to the ABI review list for,
> well, review.
[Lv Zheng]
OK.
Thanks,
-Lv
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