Re: [PATCH v10 2/3] tty: hvc: pass DMA capable memory to put_chars()
From: Greg KH <gregkh@linuxfoundation.org>
Date: 2021-10-09 11:58:48
Also in:
linuxppc-dev, lkml
Possibly related (same subject, not in this thread)
- 2021-10-14 · Re: [PATCH v10 2/3] tty: hvc: pass DMA capable memory to put_chars() · Greg KH <gregkh@linuxfoundation.org>
- 2021-10-10 · Re: [PATCH v10 2/3] tty: hvc: pass DMA capable memory to put_chars() · Greg KH <gregkh@linuxfoundation.org>
- 2021-10-09 · Re: [PATCH v10 2/3] tty: hvc: pass DMA capable memory to put_chars() · Greg KH <gregkh@linuxfoundation.org>
On Sat, Oct 09, 2021 at 07:48:28PM +0800, Xianting Tian wrote:
quoted hunk
--- a/drivers/tty/hvc/hvc_console.h +++ b/drivers/tty/hvc/hvc_console.h@@ -32,13 +32,21 @@ */ #define HVC_ALLOC_TTY_ADAPTERS 8 +/* + * These sizes are most efficient for vio, because they are the + * native transfer size. We could make them selectable in the + * future to better deal with backends that want other buffer sizes. + */ +#define N_OUTBUF 16 +#define N_INBUF 16 + +#define __ALIGNED__ __attribute__((__aligned__(sizeof(long))))
Does this conflict with what is in hvcs.c?
quoted hunk
+ 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; const struct hv_ops *ops;@@ -48,6 +56,18 @@ 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 */ + char cons_outbuf[N_OUTBUF] __ALIGNED__; + spinlock_t cons_outbuf_lock;
Did you look at the placement using pahole as to how this structure now looks?
+ + /* the buf is for putting single char to tty */ + char outchar; + spinlock_t outchar_lock;
So you have a lock for a character and a different one for a longer string? Why can they not just use the same lock? Why are 2 needed at all, can't you just use the first character of cons_outbuf[] instead? Surely you do not have 2 sends happening at the same time, right?
+ + /* the buf is for putting chars to tty */ + int outbuf_size; + char outbuf[0] __ALIGNED__;
I thought we were not allowing [0] anymore in kernel structures? thanks, greg k-h _______________________________________________ Virtualization mailing list Virtualization@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/virtualization