Homa's Maximum Message Length Modification
amjal opened this issue · comments
The maximum length of a message in Homa is set by the HOMA_MAX__MESSAGE_LENGTH macro defined in homa.h. In previous builds of the module, particularly for kernel version 5.17.7, I could just change the macro value, and it worked with larger messages.
With the newest build, however, there is an assertion error I get from this line:
#if !defined(__cplusplus)
_Static_assert(sizeof(struct homa_recvmsg_args) >= 96,
"homa_recvmsg_args shrunk");
_Static_assert(sizeof(struct homa_recvmsg_args) <= 96,
"homa_recvmsg_args grew");
#endif
I appreciate it if you explain to me why this limit is there in the first place. Is this an implementation limitation? Or is just placed for performance optimization? What is a safe way of modifying it? If these are answered somewhere in the documentation, please just direct me towards them. Thanks.
Hmmm, interesting point. This problem arose because homa_recvmsg_args
structs now contain an array of buffer pointers, which is proportional to
HOMA_MAX_MESSAGE_LENGTH.
I added the assertions on the recommendation of Dan Manjarres (cc-ed here);
I believe the reasoning is that changing the size of the struct is likely
to cause software breakage (e.g. existing application binaries will no
longer work with a new transport implementation) so this shouldn't be done
without careful thought. That said, I think it should be safe for you to
change the value 96 in the assertions to reflect the new larger
HOMA_MAX_MESSAGE_LENGTH or even comment out the assertions, as long as you
are careful to recompile all of your applications.
…-John-
On Mon, Oct 16, 2023 at 3:09 PM amjal ***@***.***> wrote:
The maximum length of a message in Homa is set by the
HOMA_MAX__MESSAGE_LENGTH macro defined in homa.h. In previous builds of the
module, particularly for kernel version 5.17.7, I could just change the
macro value, and it worked with larger messages.
With the newest build, however, there is an assertion error I get from
this line:
#if !defined(__cplusplus)
_Static_assert(sizeof(struct homa_recvmsg_args) >= 96,
"homa_recvmsg_args shrunk");
_Static_assert(sizeof(struct homa_recvmsg_args) <= 96,
"homa_recvmsg_args grew");
#endif
I appreciate it if you explain to me why this limit is there in the first
place. Is this an implementation limitation? Or is just placed for
performance optimization? What is a safe way of modifying it? If these are
answered somewhere in the documentation, please just direct me towards
them. Thanks.
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Thanks for the explanation. Commenting out the assertion and recompiling works.