[Xen-devel] [PATCH for-xen-4.5] console: increase initial conring size

[Daniel Kiper <daniel.kiper@xxxxxxxxxx>]

In general initial conring size is sufficient. However, if log
level is increased on platforms which have e.g. huge number
of memory regions (I have an IBM System x3550 M2 with 8 GiB RAM
which has more than 200 entries in EFI memory map) then some
of earlier messages in console ring are overwritten. It means
that in case of issues deeper analysis can be hindered. Sadly
conring_size argument does not help because new console buffer
is allocated late on heap. It means that it is not possible to
allocate larger ring earlier. So, in this situation initial
conring size should be increased. My experiments showed that
even on not so big machines more than 26 KiB of free space are
needed for initial messages. In theory we could increase conring
size buffer to 32 KiB. However, I think that this value could be
too small for huge machines with large number of ACPI tables and
EFI memory regions. Hence, this patch increases initial conring
size to 64 KiB.

Signed-off-by: Daniel Kiper <daniel.kiper@xxxxxxxxxx>
---
 xen/drivers/char/console.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index 2f03259..429d296 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -67,7 +67,7 @@ custom_param("console_timestamps", parse_console_timestamps);
 static uint32_t __initdata opt_conring_size;
 size_param("conring_size", opt_conring_size);
 
-#define _CONRING_SIZE 16384
+#define _CONRING_SIZE 65536
 #define CONRING_IDX_MASK(i) ((i)&(conring_size-1))
 static char __initdata _conring[_CONRING_SIZE];
 static char *__read_mostly conring = _conring;
-- 
1.7.10.4


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