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Message-ID: <57068FE4.7080005@arm.com>
Date: Thu, 7 Apr 2016 17:50:44 +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 08/14] coresight: tmc: allocating memory when needed
On 22/03/16 20:23, 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 subsytem is sollicited. Allocated buffers are
nit: *subsystem* is *solicited*.
> 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 | 97 ++++++++++++++++++++-----
> drivers/hwtracing/coresight/coresight-tmc-etr.c | 97 ++++++++++++++++++++++---
> drivers/hwtracing/coresight/coresight-tmc.c | 14 ----
> 3 files changed, 164 insertions(+), 44 deletions(-)
>
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etf.c b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> index f9749924a055..e5d67e01409c 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etf.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etf.c
> @@ -205,52 +231,75 @@ const struct coresight_ops tmc_etf_cs_ops = {
>
> int tmc_read_prepare_etf(struct tmc_drvdata *drvdata)
> {
> - int ret = 0;
> enum tmc_mode mode;
> unsigned long flags;
>
> spin_lock_irqsave(&drvdata->spinlock, flags);
>
> - /* The TMC isn't enable, so there is no need to disable it */
> - if (!drvdata->enable)
> + /* The TMC isn't enabled, so there is no need to disable it */
> + if (!drvdata->enable) {
> + /*
> + * The ETB/ETF is disabled already. If drvdata::buf is NULL
> + * trace data has been harvested.
> + */
> + if (!drvdata->buf) {
> + spin_unlock_irqrestore(&drvdata->spinlock, flags);
> + return -EINVAL;
> + }
> +
> goto out;
> + }
>
> if (drvdata->config_type != TMC_CONFIG_TYPE_ETB &&
> drvdata->config_type != TMC_CONFIG_TYPE_ETF) {
> - ret = -EINVAL;
> - goto out;
> + spin_unlock_irqrestore(&drvdata->spinlock, flags);
> + return -EINVAL;
> }
>
> /* There is no point in reading a TMC in HW FIFO mode */
> mode = readl_relaxed(drvdata->base + TMC_MODE);
> if (mode != TMC_MODE_CIRCULAR_BUFFER) {
> - ret = -EINVAL;
> - goto out;
> + spin_unlock_irqrestore(&drvdata->spinlock, flags);
> + return -EINVAL;
> }
>
> tmc_etb_disable_hw(drvdata);
> - drvdata->reading = true;
> + tmc_etb_dump_hw(drvdata);
The addition of tmc_etb_dump_hw() should have been part of the previous patch,
which made disable() reusable.
>
> out:
> + drvdata->reading = true;
Instead of spilling the spin_unlock_irq_restore() and return from too many
different places in the function above, could we do :
done:
drvdata->reading = true;
out:
> spin_unlock_irqrestore(&drvdata->spinlock, flags);
> - return ret;
> + return 0;
> }
>
> int tmc_read_unprepare_etf(struct tmc_drvdata *drvdata)
> {
...
> + }
> +
> + /* The TMC isn't enabled, so there is no need to enable it */
> + if (!drvdata->enable) {
> + /*
> + * The ETB/ETF is not tracing and the buffer was just read.
> + * As such prepare to free the trace buffer.
> + */
> + buf = drvdata->buf;
> +
> + /*
> + * drvdata::buf is switched on in tmc_read_prepare_etf() so
> + * it is important to set it back to NULL.
> + */
> + drvdata->buf = NULL;
> goto out;
> }
This check should be brought down after the MODE check below for better error
check.
>
> @@ -258,13 +307,25 @@ int tmc_read_unprepare_etf(struct tmc_drvdata *drvdata)
> mode = readl_relaxed(drvdata->base + TMC_MODE);
> if (mode != TMC_MODE_CIRCULAR_BUFFER) {
> ret = -EINVAL;
> - goto out;
> + goto err;
> }
>
> + /*
> + * The trace run will continue with the same allocated trace buffer.
> + * As such zero-out the buffer so that we don't end up with stale
> + * data.
> + */
Could this drvdata->buf be NULL here ?
> + memset(drvdata->buf, 0, drvdata->size);
> tmc_etb_enable_hw(drvdata);
> - drvdata->reading = false;
>
> out:
> + drvdata->reading = false;
> +
> +err:
> spin_unlock_irqrestore(&drvdata->spinlock, flags);
> +
> + /* Free allocated memory outside of the spinlock */
> + kfree(buf);
> +
> return ret;
> }
> diff --git a/drivers/hwtracing/coresight/coresight-tmc-etr.c b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> index 67e7d5dd891f..c4962568276e 100644
> --- a/drivers/hwtracing/coresight/coresight-tmc-etr.c
> +++ b/drivers/hwtracing/coresight/coresight-tmc-etr.c
> @@ -16,6 +16,8 @@
> */
>
> #include <linux/coresight.h>
> +#include <linux/dma-mapping.h>
> +
> #include "coresight-priv.h"
> #include "coresight-tmc.h"
>
> @@ -82,19 +84,51 @@ static void tmc_etr_disable_hw(struct tmc_drvdata *drvdata)
>
> static int tmc_enable_etr_sink(struct coresight_device *csdev, u32 mode)
> {
> + bool allocated = false;
> unsigned long flags;
> + void __iomem *vaddr;
> + dma_addr_t paddr;
> struct tmc_drvdata *drvdata = dev_get_drvdata(csdev->dev.parent);
>
> + /*
> + * 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;
> +
> spin_lock_irqsave(&drvdata->spinlock, flags);
> if (drvdata->reading) {
> spin_unlock_irqrestore(&drvdata->spinlock, flags);
> + dma_free_coherent(drvdata->dev, drvdata->size, vaddr, paddr);
> return -EBUSY;
> }
Both here and above in the etf/etb case, could we do a preliminary check
by taking the lock where we may not have to allocate the buffer and allocate
it if necessary and retake the lock ? I know it could make the code a bit more
complex, but could save us on unnecessary allocations.
Also it would be good to consolidate the return points here as well for the
error path.
>
> + /*
> + * If drvdata::buf == NULL, use the memory allocated above.
> + * Otherwise a buffer still exists from a previous session, so
> + * simply use that.
> + */
> + if (!drvdata->buf) {
> + allocated = true;
> + drvdata->vaddr = vaddr;
> + drvdata->paddr = paddr;
> + drvdata->buf = drvdata->vaddr;
> + }
> +
> + memset(drvdata->vaddr, 0, drvdata->size);
> +
> tmc_etr_enable_hw(drvdata);
> drvdata->enable = true;
> spin_unlock_irqrestore(&drvdata->spinlock, flags);
>
> + /* Free memory outside the spinlock if need be */
> + if (!allocated)
> + dma_free_coherent(drvdata->dev, drvdata->size, vaddr, paddr);
> +
> dev_info(drvdata->dev, "TMC-ETR enabled\n");
> return 0;
> }
> @@ -129,48 +163,87 @@ const struct coresight_ops tmc_etr_cs_ops = {
>
> int tmc_read_prepare_etr(struct tmc_drvdata *drvdata)
> {
> - int ret = 0;
> unsigned long flags;
>
> spin_lock_irqsave(&drvdata->spinlock, flags);
>
> - /* The TMC isn't enable, so there is no need to disable it */
> - if (!drvdata->enable)
> + /* The TMC isn't enabled, so there is no need to disable it */
> + if (!drvdata->enable) {
> + /*
> + * The ETR is disabled already. If drvdata::buf is NULL
> + * trace data has been harvested.
> + */
> + if (!drvdata->buf) {
> + spin_unlock_irqrestore(&drvdata->spinlock, flags);
> + return -EINVAL;
> + }
> +
> goto out;
> + }
>
> if (drvdata->config_type != TMC_CONFIG_TYPE_ETR) {
> - ret = -EINVAL;
> - goto out;
> + spin_unlock_irqrestore(&drvdata->spinlock, flags);
> + return -EINVAL;
> }
>
> tmc_etr_disable_hw(drvdata);
> - drvdata->reading = true;
> + tmc_etr_dump_hw(drvdata);
Same as for etf/etb, shouldn't the above dump_hw be part of the previous patch ?
>
> out:
> + drvdata->reading = true;
> spin_unlock_irqrestore(&drvdata->spinlock, flags);
> - return ret;
> + return 0;
> }
>
> int tmc_read_unprepare_etr(struct tmc_drvdata *drvdata)
> {
> int ret = 0;
> unsigned long flags;
> + void __iomem *vaddr = NULL;
> + dma_addr_t paddr;
>
> spin_lock_irqsave(&drvdata->spinlock, flags);
>
> - /* The TMC isn't enable, so there is no need to enable it */
> - if (!drvdata->enable)
> - goto out;
> -
> if (drvdata->config_type != TMC_CONFIG_TYPE_ETR) {
> ret = -EINVAL;
> + goto err;
> + }
> +
> + /* The TMC isn't enabled, so there is no need to enable it */
> + if (!drvdata->enable) {
> + /*
> + * The ETR is not tracing and trace data was just read. As
> + * such prepare to free the trace buffer.
> + */
> + vaddr = drvdata->vaddr;
> + paddr = drvdata->paddr;
> +
> + /*
> + * drvdata::buf is switched on in tmc_read_prepare_etr() and
> + * tmc_enable_etr_sink so it is important to set it back to
> + * NULL.
> + */
> + drvdata->buf = NULL;
> goto out;
> }
>
> + /*
> + * The trace run will continue with the same allocated trace buffer.
> + * As such zero-out the buffer so that we don't end up with stale
> + * data.
> + */
> + memset(drvdata->buf, 0, drvdata->size);
Are we sure drvdata->buf is not NULL here ?
Suzuki
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