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    SubjectRe: [PATCH v2 2/4] virtio_test: move magic number in code as defined constant
    On Thu, Jul 07, 2022 at 02:17:19PM +0800, Guo Zhi wrote:
    > On 2022/7/7 13:09, Michael S. Tsirkin wrote:
    > > On Thu, Jul 07, 2022 at 10:44:07AM +0800, Guo Zhi wrote:
    > > > We should avoid using magic numbers directly.
    > > Not necessarily. For repeated values - I guess.
    > > But this kind of thing:
    > >
    > > #define BUF_SIZE 1024
    > > int buf_size = BUF_SIZE;
    > >
    > > brings no benefit IMHO.
    > >
    > > And this has cost - values are now removed from code.
    >
    > Firstly, as a test, user will have to change the config to test virtio and
    > vhost frequently. If these magic number are put together like these, change
    > will be more easier.

    If tweaking these is useful for users we should add a command line flags
    as opposed to asking users to tweak code.

    > Secondly, many configs will be repeated, such as MAX_SG_FRAGS, even if some
    > varibale only appear once, subsequent upgrade of virtio_test will use these
    > variable in other place. For example, in this series of patch, patch 4/4
    > will use RINGSIZE to set INDIRECTS_BUF_SIZE.
    >
    > > > Signed-off-by: Guo Zhi <qtxuning1999@sjtu.edu.cn>

    Isn't there some way to use the size we get as 1st parameter of kmalloc?

    > > > ---
    > > > tools/virtio/virtio_test.c | 18 +++++++++++-------
    > > > 1 file changed, 11 insertions(+), 7 deletions(-)
    > > >
    > > > diff --git a/tools/virtio/virtio_test.c b/tools/virtio/virtio_test.c
    > > > index 95f78b311..1ecd64271 100644
    > > > --- a/tools/virtio/virtio_test.c
    > > > +++ b/tools/virtio/virtio_test.c
    > > > @@ -20,7 +20,10 @@
    > > > #include "../../drivers/vhost/test.h"
    > > > #define RANDOM_BATCH -1
    > > > -
    > > > +#define ALIGN 4096
    > > > +#define RINGSIZE 256
    > > > +#define TEST_BUF_NUM 0x100000
    > > > +#define BUF_SIZE 1024
    > > > /* Unused */
    > > > void *__kmalloc_fake, *__kfree_ignore_start, *__kfree_ignore_end;
    > > > @@ -100,8 +103,8 @@ static void vq_reset(struct vq_info *info, int num, struct virtio_device *vdev)
    > > > if (info->vq)
    > > > vring_del_virtqueue(info->vq);
    > > > - memset(info->ring, 0, vring_size(num, 4096));
    > > > - vring_init(&info->vring, num, info->ring, 4096);
    > > > + memset(info->ring, 0, vring_size(num, ALIGN));
    > > > + vring_init(&info->vring, num, info->ring, ALIGN);
    > > > info->vq = __vring_new_virtqueue(info->idx, info->vring, vdev, true,
    > > > false, vq_notify, vq_callback, "test");
    > > > assert(info->vq);
    > > > @@ -115,7 +118,7 @@ static void vq_info_add(struct vdev_info *dev, int num)
    > > > info->idx = dev->nvqs;
    > > > info->kick = eventfd(0, EFD_NONBLOCK);
    > > > info->call = eventfd(0, EFD_NONBLOCK);
    > > > - r = posix_memalign(&info->ring, 4096, vring_size(num, 4096));
    > > > + r = posix_memalign(&info->ring, PAGE_SIZE, vring_size(num, ALIGN));
    > > > assert(r >= 0);
    > > > vq_reset(info, num, &dev->vdev);
    > > > vhost_vq_setup(dev, info);
    > > This is actually doing more than what commit log says.
    > >
    > > > @@ -131,7 +134,7 @@ static void vdev_info_init(struct vdev_info* dev, unsigned long long features)
    > > > dev->vdev.features = features;
    > > > INIT_LIST_HEAD(&dev->vdev.vqs);
    > > > spin_lock_init(&dev->vdev.vqs_list_lock);
    > > > - dev->buf_size = 1024;
    > > > + dev->buf_size = BUF_SIZE;
    > > >
    > > >
    > > > This seems to have zero added value.
    > > >
    > Since the reason above and other magic number have been set as a defined
    > constant, change here for simplicity and consistency.
    > > > dev->buf = malloc(dev->buf_size);
    > > > assert(dev->buf);
    > > > dev->control = open("/dev/vhost-test", O_RDWR);
    > > > @@ -396,7 +399,8 @@ int main(int argc, char **argv)
    > > > done:
    > > > vdev_info_init(&dev, features);
    > > > - vq_info_add(&dev, 256);
    > > > - run_test(&dev, &dev.vqs[0], delayed, batch, reset, 0x100000);
    > > > + vq_info_add(&dev, RINGSIZE);
    > > > +
    > > > + run_test(&dev, &dev.vqs[0], delayed, batch, reset, TEST_BUF_NUM);
    > > > return 0;
    > >
    > > This replacement does not buy us anything either.
    > RINGSIZE will be used in other place in subsequent modification.
    > >
    > > > }
    > > > --
    > > > 2.17.1
    >

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