Re: [PATCH v4] misc: pci_endpoint_test: Use memcpy_toio()/memcpy_fromio() for BAR tests

From: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@linux.intel.com>
To: "Niklas Cassel" <cassel@kernel.org>,
	"Manivannan Sadhasivam" <manivannan.sadhasivam@linaro.org>,
	"Krzysztof Wilczyński" <kw@linux.com>,
	"Kishon Vijay Abraham I" <kishon@kernel.org>,
	"Arnd Bergmann" <arnd@arndb.de>,
	"Greg Kroah-Hartman" <gregkh@linuxfoundation.org>
Cc: Damien Le Moal <dlemoal@kernel.org>, linux-pci@vger.kernel.org
Subject: Re: [PATCH v4] misc: pci_endpoint_test: Use memcpy_toio()/memcpy_fromio() for BAR tests
Date: Fri, 22 Mar 2024 10:03:12 -0700	[thread overview]
Message-ID: <8dcb72ed-ee39-4fd6-a157-b7d889f35056@linux.intel.com> (raw)
In-Reply-To: <20240322164139.678228-1-cassel@kernel.org>

On 3/22/24 9:41 AM, Niklas Cassel wrote:
> The current code uses writel()/readl(), which has an implicit memory
> barrier for every single readl()/writel().
>
> Additionally, reading 4 bytes at a time over the PCI bus is not really
> optimal, considering that this code is running in an ioctl handler.
>
> Use memcpy_toio()/memcpy_fromio() for BAR tests.
>
> Before patch with a 4MB BAR:
> $ time /usr/bin/pcitest -b 1
> BAR1:           OKAY
> real    0m 1.56s
>
> After patch with a 4MB BAR:
> $ time /usr/bin/pcitest -b 1
> BAR1:           OKAY
> real    0m 0.54s
>
> Signed-off-by: Niklas Cassel <cassel@kernel.org>
> ---
> Changes since v3:
> -Use scope-based resource management __free attribute from cleanup.h to
>  avoid overly verbose gotos and labels for error handling.
> -Added a comment related to why we allocate a buffer of max 1MB.
>  (kmalloc() default upper limit is usually 4 MB on ARM and x86.)
>
>  drivers/misc/pci_endpoint_test.c | 54 +++++++++++++++++++++++++-------
>  1 file changed, 42 insertions(+), 12 deletions(-)
>
> diff --git a/drivers/misc/pci_endpoint_test.c b/drivers/misc/pci_endpoint_test.c
> index 705029ad8eb5..bf64d3aff7d8 100644
> --- a/drivers/misc/pci_endpoint_test.c
> +++ b/drivers/misc/pci_endpoint_test.c
> @@ -7,6 +7,7 @@
>   */
>  
>  #include <linux/crc32.h>
> +#include <linux/cleanup.h>
>  #include <linux/delay.h>
>  #include <linux/fs.h>
>  #include <linux/io.h>
> @@ -272,31 +273,60 @@ static const u32 bar_test_pattern[] = {
>  	0xA5A5A5A5,
>  };
>  
> +static int pci_endpoint_test_bar_memcmp(struct pci_endpoint_test *test,
> +					enum pci_barno barno, int offset,
> +					void *write_buf, void *read_buf,
> +					int size)
> +{
> +	memset(write_buf, bar_test_pattern[barno], size);
> +	memcpy_toio(test->bar[barno] + offset, write_buf, size);
> +
> +	memcpy_fromio(read_buf, test->bar[barno] + offset, size);
> +
> +	return memcmp(write_buf, read_buf, size);
> +}
> +
>  static bool pci_endpoint_test_bar(struct pci_endpoint_test *test,
>  				  enum pci_barno barno)
>  {
> -	int j;
> -	u32 val;
> -	int size;
> +	int j, bar_size, buf_size, iters, remain;
> +	void *write_buf __free(kfree) = NULL;
> +	void *read_buf __free(kfree) = NULL;

Please check the following cleanup doc. Recommendation is to avoid above __free(kfree) = NULL declarations and directly define write_buf/read_buf.

https://lore.kernel.org/lkml/171097196970.1011049.9726486429680041876.stgit@dwillia2-xfh.jf.intel.com/T/#m05d71a668ff0fad46c2055dbdcde55d7381780b7

>  	struct pci_dev *pdev = test->pdev;
>  
>  	if (!test->bar[barno])
>  		return false;
>  
> -	size = pci_resource_len(pdev, barno);
> +	bar_size = pci_resource_len(pdev, barno);
>  
>  	if (barno == test->test_reg_bar)
> -		size = 0x4;
> +		bar_size = 0x4;
>  
> -	for (j = 0; j < size; j += 4)
> -		pci_endpoint_test_bar_writel(test, barno, j,
> -					     bar_test_pattern[barno]);
> +	/*
> +	 * Allocate a buffer of max size 1MB, and reuse that buffer while
> +	 * iterating over the whole BAR size (which might be much larger).
> +	 */
> +	buf_size = min(SZ_1M, bar_size);
>  
> -	for (j = 0; j < size; j += 4) {
> -		val = pci_endpoint_test_bar_readl(test, barno, j);
> -		if (val != bar_test_pattern[barno])
> +	write_buf = kmalloc(buf_size, GFP_KERNEL);
> +	if (!write_buf)
> +		return false;
> +
> +	read_buf = kmalloc(buf_size, GFP_KERNEL);
> +	if (!read_buf)
> +		return false;
> +
> +	iters = bar_size / buf_size;
> +	for (j = 0; j < iters; j++)
> +		if (pci_endpoint_test_bar_memcmp(test, barno, buf_size * j,
> +						 write_buf, read_buf, buf_size))
> +			return false;
> +
> +	remain = bar_size % buf_size;
> +	if (remain)
> +		if (pci_endpoint_test_bar_memcmp(test, barno, buf_size * iters,
> +						 write_buf, read_buf, remain))
>  			return false;
> -	}
>  
>  	return true;
>  }

-- 
Sathyanarayanan Kuppuswamy
Linux Kernel Developer