On Thu, Oct 14, 2021 at 04:34:59PM +0800, Xianting Tian wrote:
>
> 在 2021/10/10 下午1:33, Greg KH 写道:
> > On Sat, Oct 09, 2021 at 11:45:23PM +0800, Xianting Tian wrote:
> > > 在 2021/10/9 下午7:58, Greg KH 写道:
> > > > Did you look at the placement using pahole as to how this structure now
> > > > looks?
> > > thanks for all your commnts. for this one, do you mean I need to remove the
> > > blank line? thanks
> > >
> > No, I mean to use the tool 'pahole' to see the structure layout that you
> > just created and determine if it really is the best way to add these new
> > fields, especially as you are adding huge buffers with odd alignment.
>
> thanks,
>
> Based on your comments, I removed 'char outchar', remian the position of
> 'int outbuf_size' unchanged to keep outbuf_size and lock in the same cache
> line. Now hvc_struct change as below,
>
> struct hvc_struct {
> struct tty_port port;
> spinlock_t lock;
> int index;
> int do_wakeup;
> - char *outbuf;
> int outbuf_size;
> int n_outbuf;
> uint32_t vtermno;
> @@ -48,6 +57,16 @@ struct hvc_struct {
> struct work_struct tty_resize;
> struct list_head next;
> unsigned long flags;
> +
> + /*
> + * the buf is used in hvc console api for putting chars,
> + * and also used in hvc_poll_put_char() for putting single char.
> + */
> + char cons_outbuf[N_OUTBUF] __ALIGNED__;
> + spinlock_t cons_outbuf_lock;
> +
> + /* the buf is used for putting chars to tty */
> + char outbuf[] __ALIGNED__;
> };
>
> pahole for above hvc_struct as below, is it ok for you? do we need to pack
> the hole? thanks
>
> struct hvc_struct {
> struct tty_port port; /* 0 352 */
> /* --- cacheline 5 boundary (320 bytes) was 32 bytes ago --- */
> spinlock_t lock; /* 352 4 */
> int index; /* 356 4 */
> int do_wakeup; /* 360 4 */
> int outbuf_size; /* 364 4 */
> int n_outbuf; /* 368 4 */
> uint32_t vtermno; /* 372 4 */
> const struct hv_ops * ops; /* 376 8 */
> /* --- cacheline 6 boundary (384 bytes) --- */
> int irq_requested; /* 384 4 */
> int data; /* 388 4 */
> struct winsize ws; /* 392 8 */
> struct work_struct tty_resize; /* 400 32 */
> struct list_head next; /* 432 16 */
> /* --- cacheline 7 boundary (448 bytes) --- */
> long unsigned int flags; /* 448 8 */
>
> /* XXX 56 bytes hole, try to pack */
>
> /* --- cacheline 8 boundary (512 bytes) --- */
> char cons_outbuf[16]; /* 512 16 */
> spinlock_t cons_outbuf_lock; /* 528 4 */
>
> /* XXX 44 bytes hole, try to pack */
Why not move the spinlock up above the cons_outbuf? Will that not be a
bit better?
Anyway, this is all fine, and much better than before, thanks.
greg k-h
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