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SUNRPC: Add trace event that reports reply page vector alignment
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We don't want READ payloads that are partially in the head iovec and
in the page buffer because this requires pull-up, which can be
expensive.

The NFS/RPC client tries hard to predict the size of the head iovec
so that the incoming READ data payload lands only in the page
vector, but it doesn't always get it right. To help diagnose such
problems, add a trace point in the logic that decodes READ-like
operations that reports whether pull-up is being done.

Signed-off-by: Chuck Lever <[email protected]>
Signed-off-by: Anna Schumaker <[email protected]>
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@chucklever @amschuma-ntap
chucklever authored and amschuma-ntap committed Feb 13, 2019
1 parent 5582863 commit 7be9cea
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Showing 2 changed files with 86 additions and 6 deletions.
59 changes: 59 additions & 0 deletions include/trace/events/sunrpc.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -321,6 +321,65 @@ TRACE_EVENT(rpc_xdr_overflow,
)
);

TRACE_EVENT(rpc_xdr_alignment,
TP_PROTO(
const struct xdr_stream *xdr,
size_t offset,
unsigned int copied
),

TP_ARGS(xdr, offset, copied),

TP_STRUCT__entry(
__field(unsigned int, task_id)
__field(unsigned int, client_id)
__field(int, version)
__field(size_t, offset)
__field(unsigned int, copied)
__field(const void *, head_base)
__field(size_t, head_len)
__field(const void *, tail_base)
__field(size_t, tail_len)
__field(unsigned int, page_len)
__field(unsigned int, len)
__string(progname,
xdr->rqst->rq_task->tk_client->cl_program->name)
__string(procedure,
xdr->rqst->rq_task->tk_msg.rpc_proc->p_name)
),

TP_fast_assign(
const struct rpc_task *task = xdr->rqst->rq_task;

__entry->task_id = task->tk_pid;
__entry->client_id = task->tk_client->cl_clid;
__assign_str(progname,
task->tk_client->cl_program->name)
__entry->version = task->tk_client->cl_vers;
__assign_str(procedure, task->tk_msg.rpc_proc->p_name)

__entry->offset = offset;
__entry->copied = copied;
__entry->head_base = xdr->buf->head[0].iov_base,
__entry->head_len = xdr->buf->head[0].iov_len,
__entry->page_len = xdr->buf->page_len,
__entry->tail_base = xdr->buf->tail[0].iov_base,
__entry->tail_len = xdr->buf->tail[0].iov_len,
__entry->len = xdr->buf->len;
),

TP_printk(
"task:%u@%u %sv%d %s offset=%zu copied=%u xdr=[%p,%zu]/%u/[%p,%zu]/%u\n",
__entry->task_id, __entry->client_id,
__get_str(progname), __entry->version, __get_str(procedure),
__entry->offset, __entry->copied,
__entry->head_base, __entry->head_len,
__entry->page_len,
__entry->tail_base, __entry->tail_len,
__entry->len
)
);

/*
* First define the enums in the below macros to be exported to userspace
* via TRACE_DEFINE_ENUM().
Expand Down
33 changes: 27 additions & 6 deletions net/sunrpc/xdr.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -347,13 +347,15 @@ EXPORT_SYMBOL_GPL(_copy_from_pages);
* 'len' bytes. The extra data is not lost, but is instead
* moved into the inlined pages and/or the tail.
*/
static void
static unsigned int
xdr_shrink_bufhead(struct xdr_buf *buf, size_t len)
{
struct kvec *head, *tail;
size_t copy, offs;
unsigned int pglen = buf->page_len;
unsigned int result;

result = 0;
tail = buf->tail;
head = buf->head;

Expand All @@ -367,6 +369,7 @@ xdr_shrink_bufhead(struct xdr_buf *buf, size_t len)
copy = tail->iov_len - len;
memmove((char *)tail->iov_base + len,
tail->iov_base, copy);
result += copy;
}
/* Copy from the inlined pages into the tail */
copy = len;
Expand All @@ -377,11 +380,13 @@ xdr_shrink_bufhead(struct xdr_buf *buf, size_t len)
copy = 0;
else if (copy > tail->iov_len - offs)
copy = tail->iov_len - offs;
if (copy != 0)
if (copy != 0) {
_copy_from_pages((char *)tail->iov_base + offs,
buf->pages,
buf->page_base + pglen + offs - len,
copy);
result += copy;
}
/* Do we also need to copy data from the head into the tail ? */
if (len > pglen) {
offs = copy = len - pglen;
Expand All @@ -391,6 +396,7 @@ xdr_shrink_bufhead(struct xdr_buf *buf, size_t len)
(char *)head->iov_base +
head->iov_len - offs,
copy);
result += copy;
}
}
/* Now handle pages */
Expand All @@ -406,12 +412,15 @@ xdr_shrink_bufhead(struct xdr_buf *buf, size_t len)
_copy_to_pages(buf->pages, buf->page_base,
(char *)head->iov_base + head->iov_len - len,
copy);
result += copy;
}
head->iov_len -= len;
buf->buflen -= len;
/* Have we truncated the message? */
if (buf->len > buf->buflen)
buf->len = buf->buflen;

return result;
}

/**
Expand All @@ -423,14 +432,16 @@ xdr_shrink_bufhead(struct xdr_buf *buf, size_t len)
* 'len' bytes. The extra data is not lost, but is instead
* moved into the tail.
*/
static void
static unsigned int
xdr_shrink_pagelen(struct xdr_buf *buf, size_t len)
{
struct kvec *tail;
size_t copy;
unsigned int pglen = buf->page_len;
unsigned int tailbuf_len;
unsigned int result;

result = 0;
tail = buf->tail;
BUG_ON (len > pglen);

Expand All @@ -448,18 +459,22 @@ xdr_shrink_pagelen(struct xdr_buf *buf, size_t len)
if (tail->iov_len > len) {
char *p = (char *)tail->iov_base + len;
memmove(p, tail->iov_base, tail->iov_len - len);
result += tail->iov_len - len;
} else
copy = tail->iov_len;
/* Copy from the inlined pages into the tail */
_copy_from_pages((char *)tail->iov_base,
buf->pages, buf->page_base + pglen - len,
copy);
result += copy;
}
buf->page_len -= len;
buf->buflen -= len;
/* Have we truncated the message? */
if (buf->len > buf->buflen)
buf->len = buf->buflen;

return result;
}

void
Expand Down Expand Up @@ -959,13 +974,17 @@ static unsigned int xdr_align_pages(struct xdr_stream *xdr, unsigned int len)
struct kvec *iov;
unsigned int nwords = XDR_QUADLEN(len);
unsigned int cur = xdr_stream_pos(xdr);
unsigned int copied, offset;

if (xdr->nwords == 0)
return 0;

/* Realign pages to current pointer position */
iov = buf->head;
iov = buf->head;
if (iov->iov_len > cur) {
xdr_shrink_bufhead(buf, iov->iov_len - cur);
offset = iov->iov_len - cur;
copied = xdr_shrink_bufhead(buf, offset);
trace_rpc_xdr_alignment(xdr, offset, copied);
xdr->nwords = XDR_QUADLEN(buf->len - cur);
}

Expand All @@ -977,7 +996,9 @@ static unsigned int xdr_align_pages(struct xdr_stream *xdr, unsigned int len)
len = buf->page_len;
else if (nwords < xdr->nwords) {
/* Truncate page data and move it into the tail */
xdr_shrink_pagelen(buf, buf->page_len - len);
offset = buf->page_len - len;
copied = xdr_shrink_pagelen(buf, offset);
trace_rpc_xdr_alignment(xdr, offset, copied);
xdr->nwords = XDR_QUADLEN(buf->len - cur);
}
return len;
Expand Down

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