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@xxxxxxxxxx>
> ---
> 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@xxxxxxxxxxxxxxxxxxxxxxxxx/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
