Re: [PATCH v10 2/3] tty: hvc: pass DMA capable memory to put_chars()

[Xianting Tian]

在 2021/10/14 下午4:41, Greg KH 写道:
> 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?
thanks, I will move it avove cons_outbuf, and send v11 patches soon.
> Anyway, this is all fine, and much better than before, thanks.
>
> greg k-h