Re: [PATCH v2 5/5] crypto: talitos: Add software backlog queue handling

On Thu, 5 Mar 2015 11:35:23 +0200
Horia Geantă [off-list ref] wrote:

On 3/4/2015 2:23 AM, Kim Phillips wrote:

quoted

On Tue,  3 Mar 2015 08:21:37 -0500
Martin Hicks [off-list ref] wrote:

quoted

@@ -1170,6 +1237,8 @@ static struct talitos_edesc *talitos_edesc_alloc(struct device *dev,
 						     edesc->dma_len,
 						     DMA_BIDIRECTIONAL);
 	edesc->req.desc = &edesc->desc;
+	/* A copy of the crypto_async_request to use the crypto_queue backlog */
+	memcpy(&edesc->req.base, areq, sizeof(struct crypto_async_request));

this seems backward, or, at least can be done more efficiently IMO:
talitos_cra_init should set the tfm's reqsize so the rest of
the driver can wholly embed its talitos_edesc (which should also
wholly encapsulate its talitos_request (i.e., not via a pointer))
into the crypto API's request handle allocation.  This
would absorb and eliminate the talitos_edesc kmalloc and frees, the
above memcpy, and replace the container_of after the
crypto_dequeue_request with an offset_of, right?

When scatter-gather buffers are needed, we can assume a slower-path
and make them do their own allocations, since their sizes vary
depending on each request.  Of course, a pointer to those
allocations would need to be retained somewhere in the request
handle.

Unfortunately talitos_edesc structure size is most of the times
variable. Its exact size can only be established at "request time", and
not at "tfm init time".

yes, I was suggesting a common minimum should be set in cra_init.

Fixed size would be sizeof(talitos_edesc).
Below are factors that influence the variable part, i.e. link_tbl in
talitos_edesc:
- whether any assoc / src / dst data is scattered
- icv_stashing (case when ICV checking is done in SW)

both being slow(er) paths, IMO.

Still we'd be better with:
-crypto API allocates request + request context (i.e.
sizeof(talitos_edesc) + any alignment required)
-talitos driver allocates variable part of talitos_edesc (if needed)

instead of:
-crypto API allocates request
-talitos driver allocates talitos_edesc (fixed + variable)
-memcopy of the req.base (crypto_async_request) into talitos_edesc

both in terms of performance and readability.

indeed.

At first look, the driver wouldn't change that much:
-talitos_cra_init() callback would have to set tfm.reqsize to
sizeof(talitos_edesc) + padding and also add the CRYPTO_TFM_REQ_DMA
indication in tfm.crt_flags
-talitos_edesc_alloc() logic would be pretty much the same, but would
allocate memory only for the link_tbl

I'm willing to do these changes if needed.

Please coordinate with Martin.

fwiw, caam could use this, too.

Kim