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Message-ID: <57162AA6.3030605@arm.com>
Date: Tue, 19 Apr 2016 13:55:02 +0100
From: Suzuki K Poulose <Suzuki.Poulose@....com>
To: Mathieu Poirier <mathieu.poirier@...aro.org>,
linux-arm-kernel@...ts.infradead.org
Cc: linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 07/15] coresight: tmc: allocating memory when needed
On 12/04/16 18:54, Mathieu Poirier wrote:
> In it's current form the TMC probe() function allocates
> trace buffer memory at boot time, event if coresight isn't
> used. This is highly inefficient since trace buffers can
> occupy a lot of memory that could be used otherwised.
>
> This patch allocates trace buffers on the fly, when the
> coresight subsystem is solicited. Allocated buffers are
> released when traces are read using the device descriptors
> under /dev.
>
> Signed-off-by: Mathieu Poirier <mathieu.poirier@...aro.org>
> ---
> drivers/hwtracing/coresight/coresight-tmc-etf.c | 85 +++++++++++++++++++++++--
> drivers/hwtracing/coresight/coresight-tmc-etr.c | 83 +++++++++++++++++++++++-
> drivers/hwtracing/coresight/coresight-tmc.c | 14 ----
> 3 files changed, 163 insertions(+), 19 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> index 4b8f39bd478b..7cb287ef7b9e 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> @@ -16,14 +16,12 @@
> */
>
> #include <linux/coresight.h>
> +#include <linux/slab.h>
> #include "coresight-priv.h"
> #include "coresight-tmc.h"
>
> void tmc_etb_enable_hw(struct tmc_drvdata *drvdata)
> {
> - /* Zero out the memory to help with debug */
> - memset(drvdata->buf, 0, drvdata->size);
> -
> CS_UNLOCK(drvdata->base);
>
> /* Wait for TMCSReady bit to be set */
> @@ -110,19 +108,68 @@ static void tmc_etf_disable_hw(struct tmc_drvdata *drvdata)
>
> static int tmc_enable_etf_sink(struct coresight_device *csdev, u32 mode)
> {
> + bool allocated = false;
nit: does "used" or buf_used sound more suitable than allocated ?
> + char *buf = NULL;
> unsigned long flags;
> struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>
> + /* This shouldn't be happening */
> + WARN_ON(mode != CS_MODE_SYSFS);
> +
> + /*
> + * If a buffer is already allocated *keep holding* the lock and
> + * jump to the fast path. Otherwise release the lock and allocate
> + * memory to work with.
> + */
> spin_lock_irqsave(&drvdata->spinlock, flags);
> + if (drvdata->buf)
> + goto fast_path;
> +
> + spin_unlock_irqrestore(&drvdata->spinlock, flags);
> +
> + /* Allocating the memory here while outside of the spinlock */
> + buf = kzalloc(drvdata->size, GFP_KERNEL);
> + if (!buf)
> + return -ENOMEM;
> +
> + /* Let's try again */
> + spin_lock_irqsave(&drvdata->spinlock, flags);
> +fast_path:
> if (drvdata->reading) {
> spin_unlock_irqrestore(&drvdata->spinlock, flags);
> + /*
> + * Free allocated memory outside of the spinlock. There is
> + * no need to assert the validity of 'buf' since calling
> + * kfree(NULL) is safe.
> + */
> + kfree(buf);
> return -EBUSY;
> }
We could check do the above check, before the allocation and avoid an unnecessary
alloc/free() if we really don't need that. And may be its better to get rid of the
"jump to fastpath" to avoid complicating the code, by using something like :
lock();
if (drvdata->reading) {
rc = -EBUSY;
goto unlock_out;
}
if (!drvdata->buf) {
/* Drop the lock here before allocation and retake the lock */
unlock();
alloc();
lock();
if (!buf) {
rc = -ENOMEM;
goto unlock_out;
}
}
...
> +
> tmc_etb_enable_hw(drvdata);
> drvdata->enable = true;
unlock_out:
> spin_unlock_irqrestore(&drvdata->spinlock, flags);
>
> + /* Free memory outside the spinlock if need be */
> + if (!allocated && buf)
> + kfree(buf);
> +
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> index 495540e9064d..6022ff26deba 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> @@ -16,6 +16,7 @@
> */
>
> #include <linux/coresight.h>
> +#include <linux/dma-mapping.h>
> #include "coresight-priv.h"
> #include "coresight-tmc.h"
>
> @@ -83,19 +84,69 @@ static void tmc_etr_disable_hw(struct tmc_drvdata *drvdata)
>
> static int tmc_enable_etr_sink(struct coresight_device *csdev, u32 mode)
> {
> +
> + /*
> + * If a buffer is already allocated *keep holding* the lock and
> + * jump to the fast path. Otherwise release the lock and allocate
> + * memory to work with.
> + */
> + spin_lock_irqsave(&drvdata->spinlock, flags);
> + if (drvdata->vaddr)
> + goto fast_path;
> +
> + spin_unlock_irqrestore(&drvdata->spinlock, flags);
> +
> + /*
> + * Contiguous memory can't be allocated while a spinlock is held.
> + * As such allocate memory here and free it if a buffer has already
> + * been allocated (from a previous session).
> + */
> + vaddr = dma_alloc_coherent(drvdata->dev, drvdata->size,
> + &paddr, GFP_KERNEL);
> + if (!vaddr)
> + return -ENOMEM;
> +
> + /* Let's try again */
> spin_lock_irqsave(&drvdata->spinlock, flags);
> +fast_path:
> if (drvdata->reading) {
> spin_unlock_irqrestore(&drvdata->spinlock, flags);
> + if (vaddr)
> + dma_free_coherent(drvdata->dev, drvdata->size,
> + vaddr, paddr);
> return -EBUSY;
> }
Same as above, if you move the check above before allocation, we could avoid
the alloc/free for such cases. And it would be better if simplify the code without
using the fast_path label to the middle of the code.
Otherwise, looks good.
Thanks
Suzuki
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