Re: [PATCH 08/14] coresight: tmc: allocating memory when needed

From: Mathieu Poirier
Date: Fri Apr 08 2016 - 11:23:45 EST

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On 7 April 2016 at 10:50, Suzuki K Poulose <Suzuki.Poulose@xxxxxxx> wrote:
> 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*.

Ack

>
>> released when traces are read using the device descriptors
>> under /dev.
>>
>> Signed-off-by: Mathieu Poirier <mathieu.poirier@xxxxxxxxxx>
>> ---
>> 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.

Thanks for your comment on this patchset.

After Dan found an error with the memory allocation I started to look
at the driver again and found several areas worth improving. I'm
currently re-writing this patchset and the result should be much
easier to follow. I would appreciate if you can have a look when V2
is out.

Best regards,
Mathieu

[1]. http://www.spinics.net/lists/arm-kernel/msg494888.html

>
>>
>> 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

Next message: Rui Salvaterra: "[PATCH] lib: lz4: fixed zram with lz4 on big endian machines"
Previous message: Arnaldo Carvalho de Melo: "Re: [PATCH 1/4] perf trace: Improve error message when receive non-tracepoint events"
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