D14684.id40336.diff
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D14684.id40336.diff
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	Index: sys/dev/random/randomdev.c
	===================================================================
	--- sys/dev/random/randomdev.c
	+++ sys/dev/random/randomdev.c
	@@ -130,6 +130,8 @@
	uint8_t *random_buf;
	int error, spamcount;
	ssize_t read_len, total_read, c;
	+ /* 16 MiB takes about 0.08 s CPU time on my 2017 AMD Zen CPU */
	+ const size_t sigchk_period = 16 * 1024 * 1024;

	random_buf = malloc(PAGE_SIZE, M_ENTROPY, M_WAITOK);
	p_random_alg_context->ra_pre_read();
	@@ -167,12 +169,26 @@
	read_len = MIN(read_len, PAGE_SIZE);
	p_random_alg_context->ra_read(random_buf, read_len);
	c = MIN(uio->uio_resid, read_len);
	+ /*
	+ * uiomove() may yield the CPU before each 'c' bytes
	+ * (up to PAGE_SIZE) are copied out.
	+ */
	error = uiomove(random_buf, c, uio);
	total_read += c;
	+ /*
	+ * Poll for signals every few MBs to avoid very long
	+ * uninterruptible syscalls.
	+ */
	+ if (error == 0 && uio->uio_resid != 0 &&
	+ (total_read - c) / sigchk_period !=
	+ total_read / sigchk_period)
	+ error = tsleep_sbt(&random_alg_context, PCATCH,
	+ "randrd", SBT_1NS, 0, C_HARDCLOCK);
	}
	- if (total_read != uio->uio_resid && (error == ERESTART \|\| error == EINTR))
	+ if (error == ERESTART \|\| error == EINTR) {
	/* Return partial read, not error. */
	error = 0;
	+ }
	}
	free(random_buf, M_ENTROPY);
	return (error);